Ultrasensitive fluorescence sensor for Hg2+ in food based on three-dimensional upconversion nanoclusters and aptamer-modulated thymine-Hg2+-thymine strategy

Programmable DNA Templates for Silver Nanoclusters Synthesis To Develop On-Demand FRET Aptasensor

DNA-templated silver nanoclusters (AgNCs-DNA) can be synthesized via a one-pot method bypassing the tedious process of biomolecular labeling. Appending an aptamer to DNA templates results in dual-functionalized DNA strands that can be utilized for synthesizing aptamer-modified AgNCs, thereby enabling the development of label-free fluorescence aptasensors. However, a major challenge lies in the necessity to redesign the dual-functionalized DNA strand for each specific target, thus increasing the complexity and hindering widespread application of these aptasensors. To overcome this challenge, we designed six DNA strands (DNA1-DNA6) that incorporate the templates for AgNCs synthesis and A4-linker for further aptamer coupling. Among all the synthesized AgNCs-DNA samples, it was found that both AgNCs-DNA1 and AgNCs-DNA2 stood out for their excellent long-term stability. After capturing the T4-linker that connected with aptamer1 specific for aflatoxin B1 (AFB1), however, we found that only AgNCs-DNA1/aptamer1 maintained excellent long-term stability. This finding highlighted the potential of AgNCs-DNA1 as a versatile label-free fluorescence probe for the development of on-demand fluorescence aptasensors. To emphasize its benefits in aptasensing applications, we utilized AgNCs-DNA1/aptamer1 as the fluorescence probe and MoS2 nanosheets as the quencher to develop a FRET aptasensor for AFB1 detection. This aptasensor demonstrated remarkable sensitivity, enabling the detection of AFB1 within a wide concentration range of 0.03-120 ng/mL, with a limit of detection as low as 3.6 pg/mL (S/N = 3). The versatility of the aptasensor has been validated through the recognition of diverse targets, employing aptamer2 specific for ochratoxin A and aptamer3 specific for zearalenone, thereby showcasing its extensive applicability for on-demand detection. The universal applicability of this aptasensor holds great promise for future applications in diverse fields including food safety, environmental monitoring, and clinical diagnosis.

A series of viologen complexes containing thiophene and Br- dual fluorescent chromophores for continuous visual sensing of pH and Hg2

The mercury ion (Hg2+) is a typical high-toxicity substance that can cause severe damage to the environment and human bodies. For the detection of Hg2+, there are still significant challenges in the detection range and limit of detection (LOD). In this study, three viologen-based fluorescent probes are developed, CdCl4(Btybipy) (1), ZnBr4(Btybipy) (2), CdBr4(Btybipy) (3) (Btybipy = bis-1-thiophen-3-ylmethyl-[4,4']-bipyridinyl) through conventional solvent methods for detecting pH and Hg2+. Reversible discoloration and fluorescence response behaviour in the pH range of 4-12.8 is demonstrated by viologen-based fluorescent probes, which exhibit "ON-OFF-ON" signal changes. Compared with complex 1, it is surprising to find that complexes 2-3 display both fluorescence enhancement and fluorescence quenching simultaneously with the addition of different concentrations of Hg2+ (0-20 and 25-400 μM). There is broad linearity in the range of 0-20 and 50-300 μM with LODs of 2.14 and 3.13 nM, respectively. This occurrence of dual-signal modes is attributed to the participation of Br- and the thiophene S atom as dual chromophores in the coordination reaction of Hg2+. Dual-signal mode output, high sensitivity, wide detection range, and low LODs are exhibited by these fluorescent probes. The unique coordination reaction between Br- and the thiophene S atom with Hg2+ can provide a potential strategy for the exploitation of promising sensing platforms for monitoring Hg2+.

Simple potentiometry and cyclic voltammetry techniques for sensing Hg2+ ions in water using a promising flower-shaped WS2-WO3/poly-2-aminobenzene-1-thiol nanocomposite thin film electrode

A highly promising flower-shaped WS2-WO3/poly-2-aminobenzene-1-thiol (P2ABT) nanocomposite was successfully synthesized via a reaction involving 2-aminobenzene-1-thiol, Na2WO4, and K2S2O8 as oxidants. The WS2-WO3/P2ABT nanocomposite demonstrated remarkable potential as a sensor for detecting harmful Hg2+ ions in aqueous solutions. The sensing behavior was evaluated over a wide concentration range, from 10-6 to 10-1 M, using a simple potentiometric study on a two-electrode cell. The calibration curve yielded an excellent Nernstian slope of 33.0 mV decade-1. To further validate the sensing capabilities, cyclic voltammetry was employed, and the results showed an increasing trend in the cyclic voltammetry curve as the Hg2+ concentration increased from 10-6 to 10-1 M with an evaluated sensitivity of 2.4 μA M-1. The WS2-WO3/P2ABT nanocomposite sensor exhibited exceptional selectivity for detecting Hg2+ ions, as no significant effects were observed from other interfering ions such as Zn2+, Ni2+, Ca2+, Mg2+, Al3+, and K+ ions in the cyclic voltammetry tests. Furthermore, the sensor was tested on a natural sample that was free of Hg2+ ions, and the cyclic voltammetry curves did not produce any characteristic peaks, confirming the sensor's specificity for Hg2+ detection. The sensor's cost-effectiveness and ease of fabrication present the potential for developing a simple and practical sensor for detecting highly poisonous ions in aqueous solutions.

Online trace detection of mercury ions with enhanced fluorescence excitation within metal-lined hollow-core fiber

In this Letter, we present a portable all-fiber fluorescent detection system based on metal-lined hollow-core fiber (MLHCF) for the ultra-sensitive real-time monitoring of mercury ions (Hg2+). The system employs a rhodamine derivative as the probe. The hollow core of the MLHCF serves as both the flow channel of the liquid sample and the waveguide of the optical path. The metal coating in the intermediate layer between the capillary and the polyimide (PI) coating in the MLHCF provides good light confinement, enhancing the interaction between the sample and the incident light for better fluorescence excitation and collection efficiency. Additionally, further enhancement is achieved by placing an inserted filter along the light path to reflect the excitation light back to the MLHCF. A 3-cm length of MLHCF enables simultaneous excitation of a 40-µL sample volume and collection of most of its fluorescent signal in all directions, thereby significantly contributing to its exceptional sensitivity with a limit of detection (LOD) of 2.3 ng/L. The all-fiber fluorescence-enhanced detection device also shows rapid response time, excellent reusability, and selectivity. This system presents an online, reproducible, and portable solution for the trace detection of Hg2+ and provides a promising way for detecting other heavy metal ions.