This research was supported by National Science Foundation (CCF 1814797) and University of Missouri Research Board, Material Research Center, and the College of Arts and Science at Missouri University of Science and Technology

1 . Preparation of Reagents
CAUTION: Please read and understand all relevant material safety data sheets (MSDS) before use. Some of the chemicals are toxic and volatile. Please follow special handling procedures and storage requirements. During the experimental procedure, use personal protective equipment, such as gloves, safety glasses, and a lab coat to avoid potential hazards.
<ol>
	<li>Preparation of Tris-HCl buffer
	<ol>
		<li>Dissolve 30.29 g of Tris powder in 100 mL of deionized H2O, ensure that the powder dissolves completely, and then transfer the solution to a 250 mL-volumetric flask.</li>
		<li>Add deionized H2O to the scale of 250 mL in the volumetric flask to give 1.0 M of Tris buffer.</li>
		<li>Dilute the 1.0 M Tris buffer 100 times to give 0.01 M Tris buffer and adjust the pH to 8.5 by using 1.0 M HCl standard solution.</li>
		<li>Use a pH-meter to calibrate the pH value of the 0.01 M Tris-HCl buffer.</li>
	</ol>
	</li>
	<li>Preparation of ND suspensions
	<ol>
		<li>Dilute 100 nm of monocrystalline ND suspensions (1.0 mg/mL) 50 times with the 0.01 M Tris-HCl buffer to give 0.02 mg/mL of ND suspensions.</li>
	</ol>
	</li>
	<li>Preparation of dopamine solution
	<ol>
		<li>Dissolve 20 mg of dopamine hydrochloride in 2.0 mL of 0.01 M Tris-HCl buffer to give 10 mg/mL DA solution. 
		&#8203;NOTE: The DA solution must be freshly prepared and used within 15 min.</li>
	</ol>
	</li>
	<li>Preparation of Ag[(NH3)2]OH solution
	<ol>
		<li>Dissolve 100 mg of AgNO3&#160;solid in 10 mL of deionized H2O to give 10 mg/mL AgNO3&#160;solution.</li>
		<li>Add 1.0 M ammonium hydroxide (NH3&#183;H2O) dropwise to the AgNO3&#160;solution until yellow precipitate forms, then continue to add the NH3&#183;H2O solution until the precipitation disappears. 
		NOTE: Make the minimum volume required; prepare immediately before use and dispose immediately after use. 
		CAUTION: Add NH3&#183;H2O in fume hood with face shields, gloves, and goggles.</li>
	</ol>
	</li>
</ol>
2 . Synthesis PDA Layer on the Surface of NDs (PDA-NDs)
<ol>
	<li>Add the freshly prepared DA solution (10 mg/mL) to the ND suspensions to give varied final concentrations of 50, 75, 100 &#181;g/mL of DA. Adjust the total reaction volume to 1.0 mL, transfer it to a 10 mL-test tube, and vigorously stir at 25 &#176;C, in the dark for 12 h.</li>
	<li>Centrifuge the PDA-NDs solution for 2 h at 16,000 x g, remove the supernatant and wash three times with deionized water for 1 h at 16, 000 x g each time.</li>
	<li>Re-disperse the PDA-NDs in 200 &#181;L of deionized water with sonication for 30 s. The PDA- coated NDs will be ready for further use.</li>
</ol>
3 . Reduction of AgNPs on the Surface of PDA-NDs (AgNPs-PDA-NDs)
<ol>
	<li>Dilute 40 &#181;L of the pre-synthesized PDA-NDs in Step 2.3 two times with deionized water. Add Ag[(NH3)2]OH solution to give various final concentrations of Ag[(NH3)2]+ (0.08, 0.16, 0.24, 0.40, and 0.60 mg/mL).</li>
	<li>Adjust the final volume to 100 &#181;L in a 1.5 mL-centrifuge tube by adding deionized water, followed by sonication for 10 min.</li>
	<li>Centrifuge the AgNPs-PDA-NDs for 15 min at 16,000 x g to remove the free silver ions, discard the supernatant after centrifugation, add 100 &#181;L of deionized water, and wash three times with deionized water at 16,000 x g for 5 min each time.</li>
	<li>Re-disperse the AgNPs-PDA-NDs in 100 &#181;L of deionizedwater with sonication for 30 s to prepare for further use.</li>
</ol>
4 . Analysis of PDA-NDs and AgNPs-PDA-NDs Clusters
<ol>
	<li>Ultraviolet-visible (UV) spectra
	<ol>
		<li>Use the UV spectra to monitor the average size distribution of AgNPs on PDA-ND surfaces. Transfer the AgNPs-PDA-NDs samples prepared in Step 3.4 with varied concentrations of Ag[(NH3)2]OH in 1 cm-quartz cuvette and monitor the absorption at a scan wavelength of 250 to 550 nm.</li>
	</ol>
	</li>
	<li>Transmission election microscopy (TEM)
	<ol>
		<li>Place the carbon coated copper grids on a glass slide wrapped with parafilm to keep the grids in place. Insert the glass slide with attached TEM grids into the plasma cleaner. Turn on the plasma cleaner and the vacuum pump. After 5 min, turn on the plasma and discharge the grids with a medium power level for 3 min.</li>
		<li>Deposit 5 &#181;L of the samples on the carbon film coated Cu-grids for 3 min. Use filter paper to wick off the extra sample from the edge of grid. Then, deposit a drop of deionized water on the grid for 15 s to remove salts, then wick off the water with filter paper. Repeat the washing procedure twice and allow the grid to air dry for further use.</li>
		<li>Visualize the samples by TEM, typically at 38,000X magnification. Operate at 200 KV.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Mochalin, V. N., Shenderova, O., Ho, D., Gogotsi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+properties+and+applications+of+nanodiamonds.">The properties and applications of nanodiamonds.</a> Nature Nanotechnology. 7 (1), 11-23 (2011).</li><li>Kucsko, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanometre-scale+thermometry+in+a+living+cell.">Nanometre-scale thermometry in a living cell.</a> Nature. 500 (7460), 54-58 (2013).</li><li>Liu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Origin+of+the+Robust+Catalytic+Performance+of+Nanodiamond-Graphene-Supported+Pt+Nanoparticles+Used+in+the+Propane+Dehydrogenation+Reaction.">Origin of the Robust Catalytic Performance of Nanodiamond-Graphene-Supported Pt Nanoparticles Used in the Propane Dehydrogenation Reaction.</a> ACS Catalysis. 7 (5), 3349-3355 (2017).</li><li>Chang, B. -. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+Fluorescent+Nanodiamonds+Protein-Functionalized+for+Cell+Labeling+and+Targeting.">Highly Fluorescent Nanodiamonds Protein-Functionalized for Cell Labeling and Targeting.</a> Advanced Functional Materials. 23 (46), 5737-5745 (2013).</li><li>Ho, D., Wang, C. H., Chow, E. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanodiamonds:+The+intersection+of+nanotechnology,+drug+development,+and+personalized+medicine.">Nanodiamonds: The intersection of nanotechnology, drug development, and personalized medicine.</a> Science Advances. 1 (7), 1500439 (2015).</li><li>Hsu, M. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directly+thiolated+modification+onto+the+surface+of+detonation+nanodiamonds.">Directly thiolated modification onto the surface of detonation nanodiamonds.</a> ACS Applied Materials and Interfaces. 6 (10), 7198-7203 (2014).</li><li>Krueger, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diamond+Nanoparticles:+Jewels+for+Chemistry+and+Physics.">Diamond Nanoparticles: Jewels for Chemistry and Physics.</a> Advanced Materials. 20 (12), 2445-2449 (2008).</li><li>Turcheniuk, K., Trecazzi, C., Deeleepojananan, C., Mochalin, V. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Salt-assisted+ultrasonic+deaggregation+of+nanodiamond.">Salt-assisted ultrasonic deaggregation of nanodiamond.</a> ACS Applied Materials and Interfaces. 8 (38), 25461-25468 (2016).</li><li>Akiel, R. D., Zhang, X., Abeywardana, C., Stepanov, V., Qin, P. Z., Takahashi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigating+Functional+DNA+Grafted+on+Nanodiamond+Surface+Using+Site-Directed+Spin+Labeling+and+Electron+Paramagnetic+Resonance+Spectroscopy.">Investigating Functional DNA Grafted on Nanodiamond Surface Using Site-Directed Spin Labeling and Electron Paramagnetic Resonance Spectroscopy.</a> Journal of Physical Chemistry B. 120 (17), 4003-4008 (2016).</li><li>Gaillard, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Peptide+nucleic+acid-nanodiamonds:+covalent+and+stable+conjugates+for+DNA+targeting.">Peptide nucleic acid-nanodiamonds: covalent and stable conjugates for DNA targeting.</a> RSC Advances. 4 (7), 3566-3572 (2014).</li><li>Zhang, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA-based+self-assembly+of+fluorescent+nanodiamonds.">DNA-based self-assembly of fluorescent nanodiamonds.</a> Journal of the American Chemical Society. 137 (31), 9776-9779 (2015).</li><li>Liu, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+Nanodiamond-Gold+Hybrid+Particles+for+Multimodal+Optical+and+Electron+Microscopy+Cellular+Imaging.">Fluorescent Nanodiamond-Gold Hybrid Particles for Multimodal Optical and Electron Microscopy Cellular Imaging.</a> Nano Letters. 16 (10), 6236-6244 (2016).</li><li>Lee, H., Dellatore, S. M., Miller, W. M., Messersmith, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mussel-inspired+surface+chemistry+for+multifunctional+coatings.">Mussel-inspired surface chemistry for multifunctional coatings.</a> Science. 318 (5849), 426-430 (2007).</li><li>Wang, C., Zhou, J., Wang, P., He, W., Duan, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Robust+Nanoparticle-DNA+Conjugates+Based+on+Mussel-Inspired+Polydopamine+Coating+for+Cell+Imaging+and+Tailored+Self-Assembly.">Robust Nanoparticle-DNA Conjugates Based on Mussel-Inspired Polydopamine Coating for Cell Imaging and Tailored Self-Assembly.</a> Bioconjugate Chemistry. 27 (3), 815-823 (2016).</li><li>Liu, R., Guo, Y., Odusote, G., Qu, F., Priestley, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Core-shell+Fe3O4+polydopamine+nanoparticles+serve+multipurpose+as+drug+carrier,+catalyst+support+and+carbon+adsorbent.">Core-shell Fe3O4 polydopamine nanoparticles serve multipurpose as drug carrier, catalyst support and carbon adsorbent.</a> ACS Applied Materials and Interfaces. 5 (18), 9167-9171 (2013).</li><li>Liu, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopamine+as+a+Carbon+Source:+The+Controlled+Synthesis+of+Hollow+Carbon+Spheres+and+Yolk-Structured+Carbon+Nanocomposites.">Dopamine as a Carbon Source: The Controlled Synthesis of Hollow Carbon Spheres and Yolk-Structured Carbon Nanocomposites.</a> Angewandte Chemie International Edition. 50 (30), 6799-6802 (2011).</li><li>Zeng, Y., Liu, W., Wang, Z., Singamaneni, S., Wang, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multifunctional+surface+modification+of+nanodiamonds+based+on+dopamine+polymerization.">Multifunctional surface modification of nanodiamonds based on dopamine polymerization.</a> Langmuir. 34 (13), 4036-4042 (2018).</li><li>Qin, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dopamine@Nanodiamond+as+novel+reinforcing+nanofillers+for+polyimide+with+enhanced+thermal,+mechanical+and+wear+resistance+performance.">Dopamine@Nanodiamond as novel reinforcing nanofillers for polyimide with enhanced thermal, mechanical and wear resistance performance.</a> RSC Advances. 8 (7), 3694-3704 (2018).</li><li>Barras, A., Lyskawa, J., Szunerits, S., Woisel, P., Boukherroub, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+functionalization+of+nanodiamond+particles+using+dopamine+derivatives.">Direct functionalization of nanodiamond particles using dopamine derivatives.</a> Langmuir. 27 (20), 12451-12557 (2011).</li><li>Khanal, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+Multifunctional+"Clickable"+Diamond+Nanoparticles.">Toward Multifunctional "Clickable" Diamond Nanoparticles.</a> Langmuir. 31 (13), 3926-3933 (2015).</li><li>Rad, M. H., Zamanian, A., Hadavi, S. M. M., Khanlarkhani, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Two-Stage+Kinetics+Model+for+Polydopamine+Layer+Growth.+A+Two-Stage+Kinetics+Model+for+Polydopamine+Layer+Growth.">A Two-Stage Kinetics Model for Polydopamine Layer Growth. A Two-Stage Kinetics Model for Polydopamine Layer Growth.</a> Macromolecular Chemistry and Physics. , 1700505 (2018).</li><li>Ball, V., Frari, D. D., Toniazzo, V., Ruch, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+polydopamine+film+deposition+as+a+function+of+pH+and+dopamine+concentration:+Insights+in+the+polydopamine+deposition+mechanism.">Kinetics of polydopamine film deposition as a function of pH and dopamine concentration: Insights in the polydopamine deposition mechanism.</a> Journal of Colloid and Interface Science. 386 (1), 366-372 (2012).</li><li>Liu, Y., Ai, K., Lu, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polydopamine+and+its+derivative+materials:+synthesis+and+promising+applications+in+energy,+environmental,+and+biomedical+fields.">Polydopamine and its derivative materials: synthesis and promising applications in energy, environmental, and biomedical fields.</a> Chemical Reviews. 114 (9), 5057-5115 (2014).</li><li>Hu, J., Wu, S., Cao, Q., Zhang, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+core-shell+structured+alumina/Cu+microspheres+using+activation+by+silver+nanoparticles+deposited+on+polydopamine-coated+surfaces.">Synthesis of core-shell structured alumina/Cu microspheres using activation by silver nanoparticles deposited on polydopamine-coated surfaces.</a> RSC Advances. 6 (85), 81767-81773 (2016).</li><li>Orishchin, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+Deposition+of+Uniform+Polydopamine+Coatings+on+Nanoparticle+Surfaces+with+Controllable+Thickness.">Rapid Deposition of Uniform Polydopamine Coatings on Nanoparticle Surfaces with Controllable Thickness.</a> Langmuir. 33, 6046-6053 (2017).</li><li>Gonza&#769;lez, A. L., Noguez, C., Bera&#769;nek, J., Barnard, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size,+Shape,+Stability,+and+Color+of+Plasmonic+Silver+Nanoparticles.">Size, Shape, Stability, and Color of Plasmonic Silver Nanoparticles.</a> Journal of Physical Chemistry C. 118 (17), 9128-9136 (2014).</li><li>Muthuchamy, N., Gopalan, A., Lee, K. -. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+facile+strategy+for+higher+loading+of+silver+nanoparticles+onto+silica+for+efficient+catalytic+reduction+of+4-nitrophenol.">A new facile strategy for higher loading of silver nanoparticles onto silica for efficient catalytic reduction of 4-nitrophenol.</a> RSC Advances. 5 (93), 76170-76181 (2015).</li><li>Bastus, N. G., Comenge, J., Puntes, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetically+Controlled+Seeded+Growth+Synthesis+of+Citrate-Stabilized+Gold+Nanoparticles+of+up+to+200+nm:+Size+Focusing+versus+Ostwald+Ripening.">Kinetically Controlled Seeded Growth Synthesis of Citrate-Stabilized Gold Nanoparticles of up to 200 nm: Size Focusing versus Ostwald Ripening.</a> Langmuir. 27 (17), 11098-11105 (2011).</li><li>Jana, J., Gauri, S. S., Ganguly, M., Dey, S., Pal, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver+nanoparticle+anchored+carbon+dots+for+improved+sensing,+catalytic+and+intriguing+antimicrobial+activity.">Silver nanoparticle anchored carbon dots for improved sensing, catalytic and intriguing antimicrobial activity.</a> Dalton Transactions. 44 (47), 20692-20707 (2015).</li><li>Zamudio, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+anchoring+of+silver+nanoparticles+on+N-doped+carbon+nanotubes.">Efficient anchoring of silver nanoparticles on N-doped carbon nanotubes.</a> Small. 2 (3), 346-350 (2006).</li><li>Chen, K., Li, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modification+of+membranes+with+polydopamine+and+silver+nanoparticles+formed+in+situ+to+mitigate+biofouling.">Modification of membranes with polydopamine and silver nanoparticles formed in situ to mitigate biofouling.</a> U.S. Patent Application. , (2016).</li></ol>

The authors have nothing to disclose.

This article provides a detailed protocol for the surface functionalization of NDs with self-polymerized DA coating, and the reduction of Ag[(NH3)2]+ to AgNPs on PDA layers (Figure 3). The strategy is capable of producing various thicknesses of PDA layers by simply changing the concentration of DA. The size of the AgNPs can also be controlled by altering the original concentration of metal ion solution. The TEM image in Figure 1A displays the uncoated 100 nm NDs which tended to form microclusters and aggregates. When NDs were encapsulated with PDA, the PDA layers showed as a thin ring round the NDs. The thicknesses of the PDA layers, as measured in TEM images, were around 5 nm, 10 nm, and 15 nm, which corresponded to the final DA concentrations of 50 &#181;g/mL, 75 &#181;g/mL, and 100 &#181;g/mL, respectively. The color of the NDs suspension was observed to change from colorless to dark following PDA coating, indicating the successful wrapping of PDA on ND surfaces and showing that the thickness of PDA was dependent on the concentration of DA. Please note: the critical factor that influences the DA polymerization is the pH condition (the most favorable value is 8.523). The accurate pH value of a solution is beneficial for controlling the thicknesses of PDA layers. In addition, fast agitation during polymerization is necessary for the disaggregation of NDs and the formation of a uniformed PDA layer. Therefore, this method is not effective for any particles that are unstable in alkaline solutions.
To describe the influential factors that contributed to the thickness of the PDA, we introduce equation (1) to describe the formation of a PDA layer on ND surfaces. This is based on the kinetic equation of PDA deposition on nanoparticles from previous reports21,22. The initial concentrations of DA (C1, m/v), reaction time (t), and the thickness of the PDA layer (d), are as follows:
<img alt="Equation 1" src="/files/ftp_upload/58458/58458eq1.jpg" /> (1)
R is the radius of NDs (assuming NDs are spheres), p1&#160;is the density of PDA, V1&#160;is the reaction volume, N1&#160;is the number of NDs, and k1&#160;is a constant related to pH values, partial pressure of O2, ambient temperature and luminous intensity23. Therefore, the thickness of a PDA layer can be written as equation (2)
<img alt="Equation 2" src="/files/ftp_upload/58458/58458eq2.jpg" /> (2)
Or if we rewrite equation (1) to (3):
<img alt="Equation 3" src="/files/ftp_upload/58458/58458eq3.jpg" /> (3)
Then, eliminate d3&#160;and 3d2R because d is far less than R (d&#60;&#60;R).
At last, the d can be expressed as equation (4)
<img alt="Equation 4" src="/files/ftp_upload/58458/58458eq4.jpg" /> (4)
The coating process required 12 h, with the DA being completely consumed and monitored by UV-vis spectra. Therefore, <img alt="Equation 5" src="/files/ftp_upload/58458/58458eq5.jpg" /> was a constant, and the value of d was directly proportional to the initial concentrations of DA (C1), which were confirmed by our experimental results (Table 1). Please note, along with the increase in the thicknesses of the PDA layers, accumulation speeds of the layers were slower because of the increases in the surface areas of the NDs-PDA.
The presence of the catechol groups in PDA has been shown to directly induce the growth of the nanoparticles upon the reduction of metal precursors and their immobilization on a PDA-coated surface24,25,26,27. After coating 100 nm NDs with a PDA layer (~ 15 nm), the resulting PDA-NDs were used as a substrate to synthesize AgNPs from a metal ion solution, with the assistance of sonication. As seen in Figure 2, with the increase of [Ag(NH3)2]+ concentration, the size of AgNPs increased from ~24 nm to ~28 nm, and the number of NPs raised from 97 to 117, corresponding to the [Ag(NH3)2]+ concentration of 0.4 to 0.6 mg/mL, respectively. This phenomenon can also be characterized by UV-vis spectroscopy. The absorbance peak of nanoparticles gradually appeared as the concentration of [Ag(NH3)2]+ increased (Figure 4). For example, the maximum absorbance of nanoparticles, formed by reducing 0.4 and 0.6 mg/mL of [Ag(NH3)2]+, is 410 and 430 nm, which corresponds to AgNPs with the diameters of &#8764;20 and &#8764;30 nm, respectively. This is consistent with TEM observation17.
The diameter of reduced AgNPs follows the first order linear differential equation (5), which is similar to the seeded growth synthesis of AuNPs28, where the S is the surface area of PDA-NDs, C2&#160;is the initial concentrations of Ag[(NH3)2]+, t is the reaction time, r is the radius of AgNPs, k2&#160;is a constant, p2&#160;is the density of Ag, V2&#160;is the reaction volume, N2&#160;is the number of AgNPs, and equals to S &#183; n, in which n is the average number of active catechol groups that can reduce Ag[(NH3)2]+. The AgNPs are treated as spheres:
<img alt="Equation 6" src="/files/ftp_upload/58458/58458eq6.jpg" /> (5)
In the equation, the number of AgNPs was assumed to be directly proportional to the surface area of PDA, which depended on the thicknesses of the PDA layers. On the surface of the PDA layers, the AgNPs grew with the continuous reduction of Ag[(NH3)2]+, while the metal (0) bonds at the O-site of the PDA served as the seed precursor of AgNPs. The number of AgNPs is proportional to the O-site on PDA, which is directly proportional to the surface area23,29,30,31. On the other hand, the reduced AgNPs are distributed evenly on the PDA surface because the Ag[(NH3)2]+ was reduced by the uniformed catechol groups on the PDA layers. Experimental results showed that the higher the initial concentrations of Ag[(NH3)2]+ were, the larger the AgNPs were, but with a similar number of NPs on each ND. The ratio of initial concentrations of [Ag(NH3)2]+ (C2) ratio (0.6 mg/mL : 0.4 mg/mL=1.5) were consistent with the average radius cubed [(14/12)3=1.588]. Therefore, if a higher density of particles is desired on the PDA-NDs, a thicker layer of PDA-NDs should be selected but, if larger sizes of NPs are needed, a longer reduction duration would meet the requirement.
To remove the unreacted [Ag(NH3)2]+ during the purification process, a high centrifugation speed is recommended because of the low density of NDs. The higher the centrifugation speed is, the shorter the purification duration will be, which will provide better control of the sizes of AgNPs. In addition, sonication is an indispensable approach for obtaining uniform AgNPs. Samples should be sonicated for several minutes initially before Ag[(NH3)2]+ solutions are added.
We have demonstrated a facile method for the surface modification of NDs with self-polymerized PDA. Compared with the Click Chemistry method, this strategy, not only enhances ND dispersity and stability, but also provides a reactive platform (PDA layer) for potential post-modification by reducing the metal nanoparticles or linking with amino/thiol attached species. The thickness of a PDA layer and the size of the nanoparticles on ND surfaces can be changed by varying PDA and Ag[(NH3)2]+ concentrations. They can also be used to reduce AuNPs or other noble metal NPs. By combining the diversity of PDA chemistry and the unique properties of NDs, this method will open the door for extending ND&#39;s applications in the catalyst, energy, and biomedical areas.

Nanodiamonds (NDs), a novel carbon-based material, have attracted considerable attention in recent years for use in various applications1,2. For instance, the high surface areas of NDs provide excellent catalyst support for metal nanoparticles (NPs) because of their super-chemical stability and thermal conductivity3. Furthermore, NDs play significant roles in bio-imaging, bio-sensing, and drug delivery due to their outstanding biocompatibility and nontoxicity4,5.
To efficiently extend their capabilities, it is valuable to conjugate functional species on the surfaces of NDs, such as proteins, nucleic acids, and nanoparticles6. Although a variety of functional groups (e.g., hydroxyl, carboxyl, lactone, etc.) are created on the surfaces of NDs during their purification, the conjugation yields of the functional groups are still very low because of the low density of each active chemical group7. This results in unstable NDs, which tend to aggregate, limiting further application8.
Currently, the most common methods used to functionalize NDs, are covalent conjugation by using copper-free click chemistry9, covalent linkage of peptide nucleic acids (PNA)10, and self-assembled DNA11. The non-covalent wrapping of NDs has also been proposed, including carbohydrate-modified BSA4, and HSA12coating. However, because these methods are time consuming and inefficient, it is desirable that a simple and generally applicable method can be developed to modify the surfaces of NDs.
Dopamine (DA)13, known as a natural neurotransmitter in the brain, was widely used for adhering and functionalizing nanoparticles, such as gold nanoparticles (AuNPs)14, Fe2O315, and SiO216. Self-polymerized PDA layers enrich amino and phenolic groups, which can be further utilized to directly reduce metal nanoparticles or to easily immobilize thiol/amine-containing biomolecules on an aqueous solution. This simple approach was recently applied to functionalize NDs by Qin et al. and our laboratory17,18, although DA derivatives were employed to modify NDs via Click Chemistry in earlier studies19,20.
Here, we describe a simple PDA-based surface modification method that efficiently functionalizes NDs. By varying the concentration of DA, we can control the thickness of a PDA layer from a few nanometers to tens of nanometers. In addition, the metal nanoparticles are directly reduced and stabilized on the PDA surface without the need for additional toxic reduction agents. The sizes of the silver nanoparticles depend on the initial concentrations of Ag[(NH3)2]+. This method allows the well-controlled deposition of PDA on the surfaces of NDs and the synthesis of ND conjugated AgNPs, which dramatically extends the functionality of NDs as excellent nano-platforms of catalyst supports, bio-imaging, and bio-sensors.

<table border="0" cellpadding="0" cellspacing="0" style="width:839px;" width="838">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nanodiamond</td>
			<td style="width:121px;">FND Biotech, Inc.</td>
			<td style="width:136px;">brFND-100</td>
			<td style="width:365px;">dispersed in water, and used without further purification</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dopamine hydrochloride</td>
			<td style="width:121px;">Sigma</td>
			<td style="width:136px;">H8502-25G</td>
			<td>prepare freshly</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Silver Nitrate</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:136px;">S181-25</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ammonium Hydroxide</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:136px;">A669S-500</td>
			<td>highly toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tris Hydrochloride</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:136px;">BP153-500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TEM grid carbon film</td>
			<td style="width:121px;">Ted Pella</td>
			<td style="width:136px;">01843-F</td>
			<td>300 mesh copper</td>
		</tr>
	</tbody>
</table>

bio-inspired polydopamine surface modification of nanodiamonds and its reduction of silver nanoparticles

Surface functionalization of nanodiamonds (NDs) is still challenging due to the diversity of functional groups on the ND surfaces. Here, we demonstrate a simple protocol for the multifunctional surface modification of NDs by using mussel-inspired polydopamine (PDA) coating. In addition, the functional layer of PDA on NDs could serve as a reducing agent to synthesize and stabilize metal nanoparticles. Dopamine (DA) can self-polymerize and spontaneously form PDA layers on ND surfaces if the NDs and dopamine are simply mixed together. The thickness of a PDA layer is controlled by varying the concentration of DA. A typical result shows that a thickness of ~5 to ~15 nm of the PDA layer can be reached by adding 50 to 100 &#181;g/mL of DA to 100 nm ND suspensions. Furthermore, the PDA-NDs are used as a substrate to reduce metal ions, such as Ag[(NH3)2]+, to silver nanoparticles (AgNPs). The sizes of the AgNPs rely on the initial concentrations of Ag[(NH3)2]+. Along with an increase in the concentration of Ag[(NH3)2]+, the number of NPs increases, as well as the diameters of the NPs. In summary, this study not only presents a facile method for modifying the surfaces of NDs with PDA, but also demonstrates the enhanced functionality of NDs by anchoring various species of interest (such as AgNPs) for advanced applications.

The formation of PDA layers on ND surfaces were analyzed by TEM (Figure 1). Different thicknesses of PDA layers were observed as higher concentrations of DA led to thicker PDA layers. In addition, after an encapsulating reaction, the color of the NDs solution changed from colorless to dark, while the higher the initial concentration of DA was, the darker the solution became.
Figure 2 describes the reduction of Ag[(NH3)2]+ to AgNPs on the surface of 100 nm PDA-ND surfaces. The size distribution of AgNPs, calculated by TEM, were used to determine the dependence of the original concentration of Ag[(NH3)2]+ on the sizes of the AgNPs.
The flow chart in Figure 3 presents the two-step procedure for functionalizing the surface of NDs by PDA and for reducing metal ions into NPs on the PDA-ND layers.
The formation of AgNPs on the ND surface was monitored by UV-vis spectra (Figure 4). The intensity of the peaks at ~ 400 nm increased, along with an increase in the concentration of silver solution while the peaks showed a red-shift, indicating the formation of AgNPs with increased sizes.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58458/58458fig1.jpg" /> 
Figure 1. Characterization of the thicknesses of PDA layers on the surfaces of 100 nm NDs with varied concentrations of DA (0, 50, 75, and 100 &#956;g/mL) and their corresponding TEM images. The average thicknesses of each PDA layer are ~5 nm (B), ~10 nm (C), and ~15 nm (D), respectively. The inset photograph shows the colorimetric change in the corresponding samples. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58458/58458fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58458/58458fig2.jpg" /> 
Figure 2. Characterization of AgNPs-PDA-NDs. TEM images of AgNP-PDA-NDs and the size distribution of AgNPs by adding 0.4 mg/mL (A), and 0.6 mg/mL (B) of [Ag(NH3)2]+, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58458/58458fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58458/58458fig3.jpg" /> 
Figure 3. Wall chart diagram of the surface functionalization of NDs. Two-step functionalization of the surface of NDs: (1) the surface coating of NDs with DA polymerization; (2) the reduction of metal ions into NPs on the PDA layer. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58458/58458fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58458/58458fig4.jpg" /> 
Figure 4. Characterization of reduced AgNPs on the surfaces of NDs, via UV-vis spectroscopy. This figure has been modified and reprinted by permission from Zeng et al.17. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58458/58458fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Table 1" src="/files/ftp_upload/58458/58458table1.jpg" /> 
Table 1. The thickness of PDA layer and the size of reduced AgNPs. The validation of the mathematical models with experimental data. The thickness of PDA layer is determined by the initial concentration of DA, and the ratio of initial concentrations of [Ag(NH3)2]+ is consistent with the average radius cubed of AuNPs.

Watch this Scientific Journal Video about Bio-inspired Polydopamine Surface Modification of Nanodiamonds and Its Reduction of Silver Nanoparticles at JoVE.com

Bio-inspired Polydopamine Surface Modification of Nanodiamonds and Its Reduction of Silver Nanoparticles

A facile protocol is presented to functionalize the surfaces of nanodiamonds with polydopamine.

Surface functionalization of nanodiamonds (NDs) is still challenging due to the diversity of functional groups on the ND surfaces. Here, we demonstrate a ...

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8.1K Views.  Missouri University of Science and Technology. A facile protocol is presented to functionalize the surfaces of nanodiamonds with polydopamine.

Video: Bio-inspired Polydopamine Surface Modification of Nanodiamonds and Its Reduction of Silver Nanoparticles

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

Microfluidic Dry-spinning and Characterization of Regenerated Silk Fibroin Fibers

The protocol demonstrates a method for mimicking the spinning process of silkworm. In the native spinning process, the contracting spinning duct enables the silk proteins to be compact and ordered by shearing and elongation forces. Here, a biomimetic microfluidic channel was designed to mimic the specific geometry of the spinning duct of the silkworm. Regenerated silk fibroin (RSF) spinning doped with high concentration, was extruded through the microchannel to dry-spin fibers at ambient temperature and pressure. In the post-treated process, the as-spun fibers were drawn and stored in ethanol aqueous solution. Synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) technology was used to investigate the microstructure of single RSF fibers, which were fixed to a sample holder with the RSF fiber axis normal to the microbeam of the X-ray. The crystallinity, crystallite size, and crystalline orientation of the fiber were calculated from the WAXD data. The diffraction arcs near the equator of the two-dimensional WAXD pattern indicate that the post-treated RSF fiber has a high orientation degree.

A protocol for the microfluidic spinning and microstructure characterization of regenerated silk fibroin monofilament is presented.

The protocol demonstrates a method for mimicking the spinning process of silkworm. In the native spinning process, the contracting spinning duct enables ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution of capping ligands during the synthesis reaction, their role in regulating the nucleation and growth rates of colloidal nanoparticles is not well understood. In this work, we demonstrate a mechanistic investigation of the role of trioctylphosphine (TOP) in Pd nanoparticles in different solvents (toluene and pyridine) using in situ SAXS and ligand-based kinetic modeling. Our results under different synthetic conditions reveal the overlap of nucleation and growth of Pd nanoparticles during the reaction, which contradicts the LaMer-type nucleation and growth model. The model accounts for the kinetics of Pd-TOP binding for both, the precursor and the particle surface, which is essential to capture the size evolution as well as the concentration of particles in situ. In addition, we illustrate the predictive power of our ligand-based model through designing the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can be applied to other synthesis systems and therefore serves as an effective strategy for predictive synthesis of colloidal nanoparticles.

The main goal of this work is to elucidate the role of capping agents in regulating the size of palladium nanoparticles by combining in situ small angle x-ray scattering (SAXS) and ligand-based kinetic modeling.

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution ...

High Resolution Physical Characterization of Single Metallic Nanoparticles

Individual molecules can be detected and characterized by measuring the degree by which they reduce the ionic current flowing through a single nanometer-scale pore. The signal is characteristic of the molecule&#39;s physicochemical properties and its interactions with the pore. We demonstrate that the nanopore formed by the bacterial protein exotoxin Staphylococcus aureus alpha hemolysin (&#945;HL) can detect polyoxometalates (POMs, anionic metal oxygen clusters), at the single molecule limit. Moreover, multiple degradation products of 12-phosphotungstic acid POM (PTA, H3PW12O40) in solution are simultaneously measured. The single molecule sensitivity of the nanopore method allows for POMs to be characterized at significantly lower concentrations than required for nuclear magnetic resonance (NMR) spectroscopy. This technique could serve as a new tool for chemists to study the molecular properties of polyoxometalates or other metallic clusters, to better understand POM synthetic processes, and possibly improve their yield. Hypothetically, the location of a given atom, or the rotation of a fragment in the molecule, and the metal oxidation state could be investigated with this method. In addition, this new technique has the advantage of allowing the real-time monitoring of molecules in solution.&#160;

Here, we present a protocol to detect discrete metal oxygen clusters, polyoxometalates (POMs), at the single molecule limit using a biological nanopore-based electronic platform. The method provides a complementary approach to traditional analytical chemistry tools used in the study of these molecules.

Individual molecules can be detected and characterized by measuring the degree by which they reduce the ionic current flowing through a single ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Synthesis and Characterization of Amphiphilic Gold Nanoparticles

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of their interactions with cell membranes, lipid bilayers, and viruses. The hydrophilic ligands make these particles colloidally stable in aqueous solutions and the combination with hydrophobic ligands creates an amphiphilic particle that can be loaded with hydrophobic drugs, fuse with the lipid membranes, and resist nonspecific protein adsorption. Many of these properties depend on nanoparticle size and the composition of the ligand shell. It is, therefore, crucial to have a reproducible synthetic method and reliable characterization techniques that allow the determination of nanoparticle properties and the ligand shell composition. Here, a one-phase chemical reduction, followed by a thorough purification to synthesize these nanoparticles with diameters below 5 nm, is presented. The ratio between the two ligands on the surface of the nanoparticle can be tuned through their stoichiometric ratio used during synthesis. We demonstrate how various routine techniques, such as transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and ultraviolet-visible (UV-Vis) spectrometry, are combined to comprehensively characterize the physicochemical parameters of the nanoparticles.

Amphiphilic gold nanoparticles can be used in many biological applications. A protocol to synthesize gold nanoparticles coated by a binary mixture of ligands and a detailed characterization of these particles is presented.

Gold nanoparticles covered with a mixture of 1-octanethiol (OT) and 11-mercapto-1-undecane sulfonic acid (MUS) have been extensively studied because of ...

Fabrication of Thin Film Silver/Silver Chloride Electrodes with Finely Controlled Single Layer Silver Chloride

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin film silver electrodes. Thin film silver electrodes sized 80 &#181;m x 80 &#181;m and 160 &#181;m x 160 &#181;m were sputtered on quartz wafers with a chromium/gold (Cr/Au) layer for adhesion. After passivation, polishing and cathodic cleaning processes, the electrodes underwent galvanostatic oxidation with consideration of Faraday&#39;s Law of Electrolysis to form smooth layers of AgCl with a designated degree of coverage on top of the silver electrode. This protocol is validated by inspection of scanning electron microscope (SEM) images of the surface of the fabricated Ag/AgCl thin film electrodes, which highlights the functionality and performance of the protocol. Sub-optimally fabricated electrodes are fabricated as well for comparison. This protocol can be widely used to fabricate Ag/AgCl electrodes with specific impedance requirements (e.g., probing electrodes for impedance sensing applications like impedance flow cytometry and interdigitated electrode arrays).

This paper aims to present a method to form smooth and well-controlled films of silver chloride (AgCl) with designated coverage on top of thin film silver electrodes.

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin ...

Synthesis of Functionalized Magnetic Nanoparticles, Their Conjugation with the Siderophore Feroxamine and its Evaluation for Bacteria Detection

In the present work, the synthesis of magnetic nanoparticles, its coating with SiO2, followed by its amine functionalization with (3-aminopropyl)triethoxysilane (APTES) and its conjugation with deferoxamine, a siderophore recognized by Yersinia enterocolitica, using a succinyl moiety as a linker are described.
Magnetic nanoparticles (MNP) of magnetite (Fe3O4) were prepared by solvothermal method and coated with SiO2 (MNP@SiO2) using the St&#246;ber process followed by functionalization with APTES (MNP@SiO2@NH2). Then, feroxamine was conjugated with the MNP@SiO2@NH2 by carbodiimide coupling to give MNP@SiO2@NH2@Fa. The morphology and properties of the conjugate and intermediates were examined by eight different methods including powder X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy dispersive X-Ray (EDX) mapping. This exhaustive characterization confirmed the formation of the conjugate. Finally, in order to evaluate the capacity and specificity of the nanoparticles, they were tested in a capture bacteria assay using Yersinia enterocolitica.

This work describes protocols for the preparation of magnetic nanoparticles, its coating with SiO2, followed by its amine functionalization with (3-aminopropyl)triethoxysilane (APTES) and its conjugation with deferoxamine using a succinyl moiety as a linker. A deep structural characterization description and a capture bacteria assay using Y. enterocolitica for all the intermediate nanoparticles and the final conjugate are also described in detail.

In the present work, the synthesis of magnetic nanoparticles, its coating with SiO2, followed by its amine functionalization with ...

Preparation of Silver-Palladium Alloyed Nanoparticles for Plasmonic Catalysis under Visible-Light Illumination

Localized surface plasmon resonance (LSPR) in plasmonic nanoparticles (NPs) can accelerate and control the selectivity of a variety of molecular transformations. This opens possibilities for the use of visible or near-IR light as a sustainable input to drive and control reactions when plasmonic nanoparticles supporting LSPR excitation in these ranges are employed as catalysts. Unfortunately, this is not the case for several catalytic metals such as palladium (Pd). One strategy to overcome this limitation is to employ bimetallic NPs containing plasmonic and catalytic metals. In this case, the LSPR excitation in the plasmonic metal can contribute to accelerate and control transformations driven by the catalytic component. The method reported herein focuses on the synthesis of bimetallic silver-palladium (Ag-Pd) NPs supported on ZrO2 (Ag-Pd/ZrO2) that acts as a plasmonic-catalytic system. The NPs were prepared by co-impregnation of corresponding metal precursors on the ZrO2 support followed by simultaneous reduction leading to the formation of bimetallic NPs directly on the ZrO2 support. The Ag-Pd/ZrO2 NPs were then used as plasmonic catalysts for the reduction of nitrobenzene under 425 nm illumination by LED lamps. Using gas chromatography (GC), the conversion and selectivity of the reduction reaction under the dark and light irradiation conditions can be monitored, demonstrating the enhanced catalytic performance and control over selectivity under LSPR excitation after alloying non-plasmonic Pd with plasmonic metal Ag. This technique can be adapted to a wide range of molecular transformations and NPs compositions, making it useful for the characterization of the plasmonic catalytic activity of different types of catalysis in terms of conversion and selectivity.

Presented here is a protocol for the synthesis of silver-palladium (Ag-Pd) alloy nanoparticles (NPs) supported on ZrO2 (Ag-Pd/ZrO2). This system allows for harvesting energy from visible light irradiation to accelerate and control molecular transformations. This is illustrated by nitrobenzene reduction under light irradiation catalyzed by Ag-Pd/ZrO2 NPs.