Bile-salt templated green fluorescent copper nanoclusters: detection of 4-nitrophenol in nanomolar range

Abstract

Owing to severe environmental contamination, the detection of hazardous nitro-aromatic chemicals has emerged as a potential research subject in the contemporary context. Nanomaterials are widely used in cutting-edge assays for the selective and sensitive detection of a wide range of analytes. Nanoclusters (NCs) are a novel emerging type of nanomaterials in terms of their outstanding stability and ease of fabrication. Herein, two different types of green emissive copper nanoclusters (CuNCs) were synthesized using sodium cholate (NaC) and sodium taurocholate (NaTC) as bile salts, which act as templating agents and hydrazine hydrate as a reducing agent in ambient conditions. The as-prepared CuNCs exhibited highly fluorescent, outstanding solubility in an aqueous medium and significant Stokes shift. The particle size of both CuNCs (NaC@CuNCs and NaTC@CuNCs) was examined using high-resolution transmission electron microscopy (HRTEM) analysis, which confirms their size within the 2.2–2.7 nm range. The surface functionality and chemical compositions of both CuNCs were determined using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The prepared CuNCs showed good pH stability and ionic stability. Both nanoprobes have high sensitivity and selectivity for the determination of 4-NP. The values of quantum yield and average lifetime have been evaluated to confirm the inner filter effect (IFE) quenching mechanism. Based on this, simple and accurate turn-off fluorescent nanoprobes, NaC@CuNCs and NaTC@CuNCs were created to detect 4-NP with a detection limit of 47.1 nM and 58.4 nM, respectively. Real sample analyses were performed to assess the viability of the detection technique, revealing good recovery rates and relative standard deviations towards the proposed probes. Therefore, the developed nanoprobe may be applied for on-site and fast detection of 4-NP.