Dithiothreitol-Facilitated Synthesis of Bovine Serum Albumin–Gold Nanoclusters for Pb(II) Ion Detection on Paper Substrates and in Live Cells

Abstract

In this work, a bright red fluorescent protein-capped gold nanocluster, AuNC@BSA, is developed in a green synthesis approach, and its application as a sensor for detection of Pb(II) ion in water and in live cells is demonstrated. AuNC@BSA is prepared by dithiothreitol (DTT)-mediated activation of bovine serum albumin (BSA) followed by the reduction of HAuCl 4 in an aqueous medium. The incorporation of DTT assists in the reduction of disulfide bridges present in cysteine residues, which in turn increases the reducing power of BSA forming a significant number of the Au 25 clusters that enhances the bright red fluorescence of AuNC@BSA at 660 nm when excited at 520 nm with a highest quantum yield of ∼20.0% reported so far. AuNC@BSA as nanosensor selectively detect Pb(II) ion in water with a detection limit of 1.0 ppb, lower than the World Health Organization limit (10.0 ppb), and follow quenching-based sensing mechanism through metallophilic interaction between Au(I) and Pb(II) ion. In presence of a strong chelating agent, ethylenediaminetetraacetic acid, AuNC@BSA shows regeneration ability after the treatment with Pb(II) ion. On paper-based substrate AuNC@BSA also exhibits a distinct change in red fluorescent color with metal ion concentration. The cellular study with AuNC@BSA demonstrates excellent biocompatibility that makes them a suitable candidate for biosensing of Pb(II) ion in biological medium. In HeLa cells, AuNC@BSA shows bright red fluorescence under the confocal microscope, which is quenched when incubated with Pb(II) ion enriched cells up to a limit of 1.0 ppm proving their imaging ability for in vitro applications. For the first time, such efficient green synthesis of a gold nanosensor for a sensitive and selective detection of Pb(II) ion on paper and in live cells is reported in this study.

Microwave Synthesis of Gold Nanoclusters with Garlic Extract Modifications for the Simple and Sensitive Detection of Lead Ions

“…The enhancement in the fluorescence intensity may be due to the chelation of Pb(II) ions by GE functional moieties, such as polyphenolic and flavonoid compounds. The detection limit was lower than those reported from 2018 to 2019, as listed in Table 1 [12,[20][21][22][23]. Figure 4C illustrates the selectivity of mw_G-BSA-AuNCs for the detection of Pb(II) ions versus the detection of other metal ions, such as Cu(II), Co(II), Mg(II), Hg(II), Ca(II), Mn(II), Na(I), Ba(II) Zn(II), Fe(II), Fe(III), Cr(III) and Cd(II), in the sensing platform.…”

“…Deionized water (2.5 mL) and GE [various concentrations (0-222 mg mL −1 ) for optimization, 2.5 mL] were added into the aforementioned samples, which were then sonicated for an additional 30 s for the preparation of G-BSA-AuNCs. The final mixed samples of the sonicated solutions were transferred to microwave Teflon tubes, and the microwave oven was adjusted for different reaction temperatures (50, 60, 70, 80, and 90 • C) and different reaction times (5,8,10,12,15, and 20 min), according to an optimization process. The products obtained after the microwave reactions were purified through centrifugation in a 3 K centrifugal membrane at a speed of 8000 rpm for 25 min (with an interval time of 5 min).…”

“…We optimized the synthesis conditions. The final mixtures of sonicated solutions were transferred to microwave Teflon tubes for a microwave reaction at 70 • C (100 W) for different reaction times (5,8,10,12,15, and 20 min). The obtained products were purified.…”

“…Most BSA-AuNC preparations require at least several hours, even if the preparation methods are matured. These preparations are commonly used for metal ion detection in methods of quenching (turning off) fluorescence [9,12]. Developing alternative methods for the rapid and green preparation of BSA-AuNCs is essential for sensitive heavy metal detection in analytical applications.…”

Selection of Graphite Pencil Grades for the Design of Suitable Electrodes for Stacking Multiple Single‐Inlet Paper‐Pencil Fuel Cells

“…This self‐pumping property along with its low cost and easy availability makes the paper an attractive substrate for point‐of‐care diagnostics devices, environmental contamination monitoring including energy generation . Recently, we have reported paper‐based microfluidic fuel cells, energy harvesting devices, field effect transistors, supercapacitors, active micro‐mixers and sensing for detection of contaminations in water and biological medium …”