Development of a near infrared Au–Ag bimetallic nanocluster for ultrasensitive detection of toxic Pb²⁺ ions in vitro and inside cells

Abstract

Although the research activities pertaining to the synthesis of fluorescent noble metal nanoclusters (NCs) and their applications in biological optics have been growing, only limited information is available in the near IR (NIR) region. However, fluorescence spectroscopy and microscopy in the NIR region offer significant advantages over UV and visible wavelengths. In this manuscript, we demonstrate biomineralized synthesis of stable Au-Ag bimetallic NCs with tunable NIR fluorescence using bovine serum albumin (BSA) as a protein template. We also demonstrate its application in the detection of toxic heavy metal ions Pb 2+ in vitro and inside cells. The tunability of the fluorescence emission between 680 nm and 815 nm is achieved by systematically varying the ratio of Au and Ag in the composite NCs. The bimetallic NCs when interacting with Pb 2+ offered a large increase in fluorescence intensity, which enabled sensitive detection of Pb 2+ . We determined a limit of detection (LOD) of 96 nM for the detection of Pb 2+ under in vitro conditions, which is significantly less than the safe level in drinking water. Its applicability has also been demonstrated successfully in real water samples collected from local water bodies. † Electronic supplementary information (ESI) available: Two additional tables describing the synthetic optimization in terms of Au/Ag molar ratio variations and time resolved study with respect to Au/Ag variation have been mentioned. Absorption spectra of (Au-Ag@BSA) opt NCs; MALDI mass spectrum of the nanoclusters; X-ray photoelectron spectra; uorescence stability of nanoclusters in the presence of EDTA, NaCl and different pH; stability of (Au-Ag@BSA) opt NCs with time; variation of nanocluster uorescence intensity with increasing Ag concentration. See

Controllable Synthesis of Bimetallic Nanostructures Using Biogenic Reagents: A Green Perspective

“…The fluorescence spectra of BSA-stabilized Au–Ag nanoclusters with different alloy compositions are shown in Figure a . A systematic shifting of the emission peak position toward the NIR region can be seen with the increasing Ag mole fraction.…”

“…Furthermore, the sulfur-containing amino acid residues (e.g., cysteine, methionine) in BSA were identified as key players in the nucleation, growth, and stabilization of the nanoclusters of Au . With the goal of achieving enhanced and tunable emission properties, several groups have delved into the synthesis of bimetallic Au–Ag nanoclusters using BSA. − In a typical synthesis, the Au 3+ and Ag + precursors are incubated with BSA at the physiological temperature (37 °C) under alkaline conditions, and the reaction is allowed to proceed for several hours (≥12 h). , The reaction time can be dramatically reduced through heating. It is likely that the denaturation of protein at elevated temperatures exposes more of the protein’s reducing functionalities, and this leads to an accelerated reaction rate.…”

“…(c) Extent of fluorescence intensity enhancement in the presence of different metal ions. Reproduced from ref . Copyright 2019.…”

“…94−97 In a typical synthesis, the Au 3+ and Ag + precursors are incubated with BSA at the physiological temperature (37 °C) under alkaline conditions, and the reaction is allowed to proceed for several hours (≥12 h). 94,96 The reaction time can be dramatically reduced through heating. It is likely that the denaturation of protein at elevated temperatures exposes more of the protein's reducing functionalities, and this leads to an accelerated reaction rate.…”

Bio-Mediated Synthesis of Nanoparticles for Fluorescence Sensors

“…Its applicability has also been confirmed effectively in real water samples poised from local water bodies. 112 Song et al described molecule of vancomycin was engaged as reducer/stabilizer for facile one-pot synthesis of water revealed a bluish fluorescence emission at 410 nm within a short synthesis time about 50 min. Based on the strong fluorescence quenching due to electron transfer mechanism by the outline of ferric ions (Fe 3+ ), the Van-AuNCs were remarkably intended for sensitive and selective detecting Fe3+ with a limit of 1.4 µmol L -1 in the linear range of 2-100 µmol L -1 within 20 minutes.…”