Comparative and Selective Interaction of Amino Acid d-Cysteine with Colloidal Gold Nanoparticles in the Presence of a Fluorescent Probe in Aqueous Medium

Abstract

In this communication, we report the comparative and selective interaction of amino acid d -cysteine ( d -Cys) with citrate caped gold nanoparticles (Au NPs) in the presence of a fluorescent dye, rhodamine B (RhB), in aqueous solution. Au NPs of size 27.5 nm could almost fully quench the steady-state fluorescence emission of RhB at their optimum concentrations in the mixed solution. The interactions of d -Cys, l -Cys, all other relevant d - and l -amino acids, neurotransmitters, and other relevant biological compounds with the Au NPs/RhB mixed solution have been explored by monitoring the fluorescence recovery efficiencies from the almost fully quenched state of RhB fluorescence via a simple steady-state spectrofluorometric method. The higher fluorescence recovery for the interaction of d -Cys with the Au NPs/RhB mixed system is accompanied by a distinct color change (red-wine to bluish-black) of the assay medium after the reaction compared to that of all other interfering compounds considered in this work. The sensitivity of this fluorometric response lies in a broad linear range of concentrations of d -Cys and the limit of detection (LOD) is found to be 4.2 nM, which is low compared to many other methods available in the literature. The different degrees of interaction of d -Cys and l -Cys with the Au NPs/RhB mixed sample have been further explored by circular dichroism (CD) spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The selective interaction of d -Cys with the proposed Au NPs/RhB mixed system is also found to be correlated with interparticle cross-linking and aggregations of nanoparticles by the analysis of ζ potential and dynamic light scattering (DLS) study, transmission electron microscopy (TEM), atomic force microscopy (AFM), UV–vis absorption spectroscopy etc. The proposed interaction mechanism is further studied with a normal human urine sample to elucidate that the optimized combination of Au NPs and RhB may be realized as an efficient platform for detection of the amino acid d -Cys in a real biosample via a simple fluorometric approach.

Enhancement of Fluorescence Mediated by Silver Nanoparticles: Implications for Cell Imaging

“…Interestingly, on further increase in Ag NP concentrations in the mixed solution, the fluorescence intensity starts to decrease as shown in Figure b. The apparent binding constant ( K A ) and number of binding sites ( n b ) for the Ag NP/FL mixed solution are computed by using the linear Benesi–Hildebrand (BH) equation Log { F − F 0 F 0 } = Log ( K A ) + n normalb Log [ Q ] where F 0 and F are the steady-state fluorescence emission intensities of FL in the absence and presence of Ag NPs, respectively.…”

“…This high value of K eq corresponds to the strong binding interaction between FL and CTAB in the 1:2 binding stoichiometry. The magnitude of K eq is also related to the change in Gibbs free energy (Δ G ) during complexation between the species and is estimated using the equation Δ G = – RT ln K eq , where R is the universal gas constant and T is the absolute temperature. Both the values of K eq and Δ G at ambient temperature (298 K) confirm the binding of FL with the micellar surface of CTAB in the aqueous solution .…”

“…The values of K A and n b are obtained from the intercept and slope of the plot of Log­{( F – F 0 )/ F 0 } vs Log­[ Q ] as shown in the inset of Figure b and are presented in Table . The Gibbs free energy (Δ G 0 ) for the Ag NP/FL mixed solution at 298 K is also calculated using the following expression: Δ G 0 = – RT ln K A , where R is the universal gas constant and T is the absolute temperature. The calculated value of Δ G 0 is presented in Table .…”

“…The apparent binding constant (K A ) and number of binding sites (n b ) for the Ag NP/FL mixed solution are computed by using the linear Benesi− Hildebrand (BH) equation. 50 =…”

Development of Novel Peptide-Modified Silver Nanoparticle-Based Rapid Biosensors for Detecting Aminoglycoside Antibiotics

“…These results demonstrates the high specificity of CHP@AgNPs toward AGAs, as they did not exhibit any colorimetric or spectral response when interacting with nontarget antibiotics. Notably, the tested AGAs, including dihydrostreptomycin, streptomycin, neomycin, amikacin, gentamicin, tobramycin, and kanamycin, were found to induce immediate aggregation of CHP@AgNPs via coupling between adjacent peptide groups, consistent with the previous report . Furthermore, additional experiments were performed to validate the high specificity of CHP@AgNPs and confirm its potential as a versatile and reliable analytical platform for detecting the entire class of AGAs (see the Supporting Information).…”