Ultrasensitive and highly selective Co2+ detection based on the chiral optical activities of L-glutathione-modified gold nanoclusters

Abstract

Developing highly sensitive and selective detection methods is crucial for environmental and healthcare monitoring. In this study, the chiral and fluorescent signals of L-glutathione-modified gold nanoclusters (L-GSH-Au NCs) were discovered to be responsive to Co²⁺, which displayed linear correlations with the concentration changes of Co²⁺. Notably, the chiral signal was more sensitive than the FL signal, whose limit of detection (LOD) was calculated to be 0.37 μM and 3.93 times lower than the LOD obtained with fluorescent signals. Moreover, the chiral signals exhibited unexpectedly high selectivity towards Co²⁺, effectively avoiding interference from other metal ions and biomolecules. Furthermore, the concentrations of Co²⁺ in various samples, such as Taihu water, tap water, bottled water, and animal serum, were accurately quantified using the chiral signals of L-GSH-Au NCs without complex pretreatment, with recoveries ranging between 95.64% and 103.22%. This study not only provides an innovative approach for Co²⁺ detection but also highlights the detection capabilities of chiral signals in complex environments.

Keywords: chirality; cobalt ion; detection; fluorescence; nanoclusters.

SCHEME 1

Scheme of Co²⁺ detection based on the chiral and fluorescent signals of L-GSH stabilized Au NCs.

FIGURE 1

Transmission electron microscopy (TEM) images of (A) L-GSH-Au NCs and (B) L-Co-GSH-Au NCs (the insets show the size distribution histogram of L-GSH-Au NCs and L-Co-GSH-Au NCs). (C) Circular dichroism (CD) spectra and (D) fluorescence (FL) spectra of L-GSH-Au NCs and L-Co-GSH-Au NCs (Excitation wavelength: 405 nm). The final concentration of Co²⁺ is 500 μM for preparing the sample of L-Co-GSH-Au NCs.

FIGURE 2

High-resolution X-ray photoelectron spectroscopy (XPS) spectra of (A) Co 2p, (B) O 1s, and (C) N 1s in L-GSH-Au NCs and L-Co-GSH-Au NCs. (D) The Fourier transform infrared spectroscopy of L-GSH-Au NCs (black), and L-Co-GSH-Au NCs (red).

FIGURE 3

(A) Circular dichroism (CD) and (B) fluorescence (FL) of L-Co-GSH-Au NCs with the concentration of Co²⁺ changing from 0 to 1,000 μM (Excitation wavelength: 405 nm). (C) The CD intensity of L-Co-GSH-Au NCs at 645 nm and (D) the FL intensity of L-Co-GSH-Au NCs at 720 nm with Co²⁺ concentration ranging from 0 to 1,000 μM. The inset images in (C, D) are captured under daylight and UV light irradiation, respectively. Data are presented as mean ± standard deviation (n = 3). The linear relationships between (E) the CD intensity at 645 nm and the logarithm of Co²⁺ concentrations (logCco²⁺), and (F) the FL intensity at 720 nm and the logarithm of Co²⁺ concentrations. Data are presented as mean ± standard deviation (s.d.) (n = 3).

FIGURE 4

CD intensity at 645 nm and FL intensity at 720 nm of metal ions and biological interferences (500 μM) treated L-GSH-Au NCs, data are presented as mean ± s.d. (n = 3).