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The trifunctional l-cysteine containing carboxylic acid, amine and thiol is chemisorbed on the gold electrode surface via the thiol groups to form the self-assembled monolayer. Then the bilayer is assembled stepwise on the cysteine modified gold electrode. A layer of 3-marcaptopropionic acid functionalized silver nanoparticles is covalently coupled with amine group of cysteine and other layer of amine functional group containing biotin or avidin molecules is covalently coupled with carboxylic acid functional groups of cysteine. The improvement of electrochemical properties are noted for the cysteine modified gold electrode coupled with biomolecules first followed by coupling with the functionalized silver nanoparticles. This modified gold electrode is used to study the electrochemical sensing response of respective complementary biomolecule immobilized gold electrode towards the biotin or avidin. As revealed the avidin modified electrode is found to have better sensing performances toward biotin in terms of sensitivity and detection limit over the other one. The sensitivity of 1.243 Ω (ng)-1 L mm-2 and detection limit of 1.4 × 10−3 ng/L is observed for avidin sensing on biotin layer. For biotin sensing on avidin layer a sensitivity of 6.143 Ω (ng)-1 L mm-2 and detection limit of 1.2 × 10−5 ng/L is obtained from the calibration plot.

Justyna Hajtuch,1 Nadhim Hante,2 Ewelina Tomczyk,3 Michal Wojcik,3 Marek Witold Radomski,4 Maria Jose Santos-Martinez,2 Iwona Inkielewicz-Stepniak1 1Department of Medical Chemistry, Medical University of Gdansk, Gdansk, Poland; 2School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin, Dublin 2, Ireland; 3Faculty of Chemistry, University of Warsaw, Warsaw, Poland; 4Department of Anatomy, Physiology and Pharmacology, University of Saskatchewan, Saskatoon, CanadaCorrespondence: Maria Jose Santos-MartinezSchool of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin, Dublin 2, IrelandTel +353 1 896 4281Fax +353 1 608 2821Email santosmm@tcd.ieIwona Inkielewicz-StepniakDepartment of Medical Chemistry, Medical University of Gdansk, Debinki 1 St. Gdansk 80-211, PolandTel +48 58 349 1450Fax +48 58 349 1450Email iinkiel@gumed.edu.plPurpose: We studied the effects of silver nanoparticles (AgNPs) on human blood platelet function. We hypothesized that AgNPs, a known antimicrobial agent, can be used as blood-compatible, “ideal material’’ in medical devices or as a drug delivery system. Therefore, the aim of the current study was to investigate if functionalized AgNPs affect platelet function and platelets as well as endothelial cell viability in vitro.Methods: AgNPs, functionalized with reduced glutathione (GSH), polyethylene glycol (PEG) and lipoic acid (LA) were synthesized. Quartz crystal microbalance with dissipation was used to measure the effect of AgNPs on platelet aggregation. Platelet aggregation was measured by changes in frequency and dissipation, and the presence of platelets on the sensor surface was confirmed and imaged by phase contrast microscopy. Flow cytometry was used to detect surface abundance of platelet receptors. Lactate dehydrogenase test was used to assess the potential cytotoxicity of AgNPs on human blood platelets, endothelial cells, and fibroblasts. Commercially available ELISA tests were used to measure the levels of thromboxane B2 and metalloproteinases (MMP-1, MMP-2) released by platelets as markers of platelet activation.Results: 2 nm AgNPs-GSH, 3.7 nm AgNPs-PEG both at 50 and 100 μg/mL, and 2.5 nm AgNPs-LA at 100 μg/mL reduced platelet aggregation, inhibited collagen-mediated increase in total P-selectin and GPIIb/IIIa, TXB2 formation, MMP-1, and MMP-2 release. The tested AgNPs concentrations were not cytotoxic as they did not affect, platelet, endothelial cell, or fibroblast viability.Conclusion: All tested functionalized AgNPs inhibited platelet aggregation at nontoxic concentrations. Therefore, functionalized AgNPs can be used as an antiplatelet agent or in design and manufacturing of blood-facing medical devices, such as vascular grafts, stents, heart valves, and catheters.Keywords: functionalized silver nanoparticles, blood platelets, QCM-D, platelets receptors, TXB2, MMP-1 and MMP-2

A gold electrode was modified with cysteamine by a self-assembly monolayer technique and covalently coupled with 3-mercaptopropionic acid functionalized silver nanoparticles. The free carboxylic acid groups of the 3-mercaptopropionic acid functionalized silver nanoparticles assembled on gold electrode were bonded with the amine groups of biotin or avidin trough amide linkages. The changes in the interfacial properties of gold electrode modified stepwise were examined by cyclic voltammetry and electrochemical impedance spectroscopy using the ferric/ferrous redox system. The electrochemical sensing properties of covalently bonded biotin or avidin on a gold electrode modified with silver nanoparticle were studied by cyclic voltammetry and electrochemical impedance spectroscopy by the varying concentrations of the bio-affinity molecules in the same redox system. The charge transfer resistance was directly proportional to the concentration of analyte while the response was weakly dependent upon the change in the respective peak anodic currents. The sensing mechanism was established to explain the role of the silver nanoparticles. [ABSTRACT FROM AUTHOR]

In this work primarily one-pot synthetic development in the preparation of clopidogrel bisulfate with a polymorphic crystalline form II in 90% yield was developed. This premade antiplatelet drug has been used to protect starch-stabilized silver nanoparticles (AgNPs). [ABSTRACT FROM AUTHOR]

The [3+2] cycloaddition reaction between nitroolefins and alkyl/aryl azides was studied using functionalized silver nanoparticles (FnAgNPs) of average diameter 23 ± 1 nm as catalyst produced by the plant extract Protorhus longifolia. We found FnAgNPs to catalyze the reactions efficiently yielding a series of 1,5-disubstituted-1,2,3-triazolines under mild reaction conditions with no side products. The catalytic activity of FnAgNPs was compared with naked AgNPs and FnAgNPs found to be very effective. Except solvents, the whole experiments do not require any chemical/reagent which makes the process green. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A chemiluminescence (CL) sensing method for amino acid discrimination based on luminol functionalized silver nanoparticles (LumAgNPs) has been developed. Luminescence emission in the presence of hydrogen peroxide under neutral conditions was characterized in three ways: the time required for the signal to appear (Ta), the time required to reach maximum luminescence (Tp), and CL intensity. These factors were found to change upon interaction of the nanoparticles with various amino acids, leading to distinct response patterns characteristic of each analyte. Seven amino acids (l-cysteine, l-proline, l-phenylalanine, l-arginine, l-threonine, l-gluTamic acid, and l-tyrosine) were identified at a concentration of 10 ng/mL. This sensitivity is about 3 orders of magnitude better than that of recently reported methods based on fluorescent sensor arrays using cucurbit[n]uril and comparable to high-performance liquid chromatography. Application to 27 unknown samples gave a 96.3% success rate at the 10 ng/mL level. [ABSTRACT FROM AUTHOR]

The interaction of novel polyvinylthiol coated silver nanoparticles (Ag-PVT) with human serum albumin (HSA) has been investigated by fluorescence (intrinsic, extrinsic and synchronous), UV–visible, and circular dichroism spectroscopies. Analysis of the fluorescence quenching data of HSA by Ag-PVT nanoparticles using Stern–Volmer method revealed the formation of 1:1 ground state complex. Evaluation of binding parameters and binding energy indicated that the binding reaction was exothermic. On the basis of fluorescence measurements it was concluded that hydrophobic forces play crucial role in stabilizing the complex. The binding distance was calculated by using Förster resonance energy transfer (FRET) theory. The conformational changes of HSA were obtained qualitatively as well as quantitatively using synchronous fluorescence and CD, respectively. The HSA underwent partial unfolding in presence of Ag-PVT nanoparticles. [ABSTRACT FROM AUTHOR]

Silver nanoparticles were functionalized with polyvinylthiol (Ag-PVT) and their effect on the conformation of hen-egg white lysozyme was seen by means of spectroscopic techniques, viz. , UV visible, fluorescence (intrinsic and synchronous), resonance Rayleigh scattering and circular dichroism. UV absorption spectra of lysozyme show a hyperchromic shift on the addition of Ag-PVT nanoparticles indicating the complex formation between the two. The interaction between lysozyme and Ag-PVT nanoparticles was takes place via static quenching with 1:1 binding ratio as revealed by the analysis of fluorescence measurements. Circular dichroism spectroscopic data show a decrease in α-helical content of lysozyme on interaction with Ag-PVT nanoparticles which was due to the partial unfolding of the protein. Synchronous fluorescence spectroscopy disclosed that the microenvironments of both tryptophan and tyrosine residues were perturbed in the presence of Ag-PVT nanoparticles and perturbation in the tryptophan environment was more prominent. Rayleigh scattering (RRS) intensity increases on increasing the Ag-PVT nanoparticles concentration till it reaches to the saturation. The RRS intensity increases four times as compared to the native protein indicating the possibility of protein aggregation at higher concentrations of nanoparticles. [ABSTRACT FROM AUTHOR]

Highly selective label free colorimetric sensor based on AgNPs stabilized by phenolic chelating ligand, N , N ′-bis(2-hydroxybenzyl)-1,2-diaminobenzene (1), for NO 2 − anions has been developed. Addition of NO 2 − showed selective decolourisation of brownish yellow colour of 1-AgNPs with the detection limit of 10 −7 M. Absorption studies showed the complete disappearance of 1-AgNPs peak at 426 nm due to the conversion of AgNPs to silver ions. The presence silver ions were confirmed by white precipitates of AgCl formation with NaCl. The interference studies confirmed the high selectivity of NO 2 − sensing in presence of anions as well as cations by 1-AgNPs. A linear relationship was observed between the change of absorption and concentration of NO 2 − . The present approach could be performed at room temperature and ambient conditions. The practical applications of 1-AgNPs for selective sensing of NO 2 − in different water samples such as ground, river, pond and tap water have also been demonstrated. [ABSTRACT FROM AUTHOR]

• AgNO 3 and AgNps-Cit- L -Cys reduce plant growth and Chl content increasing MDA amount. • L. minuta shows more limited growth, higher chlorosis and stress levels than L. minor. • AgNPs-Cit- L -Cys cause much less alteration compared to AgNO 3 on both species. • AgNPs-Cit- L -Cys, has potential in reducing phytotoxicity of AgNPs in aquatic systems. Duckweeds are aquatic plants often used in phytotoxic studies for their small size, simple structure, rapid growth, high sensitivity to pollutants and facility of maintaining under laboratory conditions. In this paper, induced phytotoxic effects were investigated in Lemna minor and Lemna minuta after exposition to silver nitrate (AgNO 3) and silver nanoparticles stabilized with sodium citrate and L -Cysteine (AgNPs-Cit- L -Cys) at different concentrations (0, 20 and 50 mg/L) and times (7 and 14 days). Lemna species responses were evaluated analyzing plant growth (mat thickness, fresh and dry biomass, relative growth rate – RGR) and physiological parameters (chlorophyll – Chl, malondialdehyde – MDA, ascorbate peroxidase – APX and catalase - CAT). Ag content was measured in the fronds of the two Lemna species by inductively coupled plasma optical emission spectrometry. AgNO 3 and AgNPs-Cit- L -CYs produced phytotoxic effects on both duckweed species (plant growth and Chl reduction, MDA increase) that enhanced in response to increasing concentrations and exposure times. AgNPs-Cit- L -Cys caused much less alteration in the plants compared to AgNO 3 suggesting that the presence of bifunctionalized AgNPs-Cit- L -Cys have a reduced phytotoxic effect as compared to Ag+ released in water. Based on the physiological performance, L. minuta plants showed a large growth reduction and higher levels of chlorosis and stress in respect to L. minor plants, probably due to greater Ag+ ions accumulation in the fronds. Albeit with some differences, both Lemna species were able to uptake Ag+ ions from the aqueous medium, especially over a period of 14 days, and could be considered adapt as phytoremediation agents for decontaminating silver ion-polluted water. [ABSTRACT FROM AUTHOR]