Combination of Capped Gold Nanoslit Array and Electrochemistry for Sensitive Aqueous Mercuric Ions Detection

Optical fiber fluorescence Cu2+ sensing technology based on CdSe/ZnS quantum dots: Large detection range, low detection limit

BACKGROUND

Copper ion (Cu2+), a crucial heavy metal ion, is closely associated with human health and the ecological environment. Imbalances in Cu2+ can result in health issues for humans and damage to the ecosystem. Therefore, it is essential to detect Cu2+ in the environment. However, current Cu2+ sensors still face challenges such as limited detection range, poor detection limits, high costs, and complex preparation processes. Clearly, there is a need for a Cu2+ sensor with an extensive detection range, low detection limit, cost-effectiveness, and simple preparation methods that enable online monitoring and real-time measurement of Cu2+.

RESULTS

In this paper, a high-performance optical fiber fluorescent Cu2+ sensor based on polyethylene glycol diacrylate (PEGDA) hydrogel encapsulated CdSe/ZnS quantum dots (QDs) is designed and fabricated. Due to the porous nature of PEGDA hydrogels, large-diameter CdSe/ZnS QDs are confined within the hydrogels, while small molecules Cu2+ are allowed to permeate them. Cu2+ reacts with QDs, resulting in the fluorescence quenching of QDs, which enables the detection of Cu2+. Experimental results show that the sensor can quantitatively analyze Cu2+ in the concentration range of 0.1-200 μM, with a limit of detection (LOD) of only 0.8 nM, and the fastest response time is only 5 s. Additionally, the sensor exhibits strong specificity, has been successfully applied to real water sample detection, demonstrates good stability, and shows great potential for real-time Cu2+ detection.

SIGNIFICANCE

The sensor possesses a large detection range and low LOD, and the synthesis of its core fluorescent probe is straightforward and expedient. Specifically, the fluorescent probe can be synthesized by subjecting a solution of hydrogel precursors doped with CdSe/ZnS QDs to UV irradiation for approximately 2 min. This method is particularly suitable for monitoring confined environments and holds significant implications for the production of Cu2+ sensors capable of real-time detection.

Real-Time Plasmonic Strain Sensors Based on Surface Relief Diffraction Gratings

Large-scale diffraction gratings were fabricated in surface relief on azobenzene thin films and transferred to flexible PDMS substrates using soft lift-off lithography. The PDMS gratings were strained along the grating vector axis and the resulting surface topography was analyzed using diffraction angle measurements, AFM imagery and surface plasmon resonance (SPR) spectra. All measurement methods exhibited a linear response in strain indicating the useability of these sensors in real-world applications. For SPR-based strain sensing, an increasing pitch and a decreasing modulation depth were observed with increasing strain. The SPR peak shifted by ~1.0 nm wavelength and the SPR intensity decreased by ~0.3 a.u. per percentage of applied strain. The tested PDMS samples retained their integrity even after multiple cycles of stretching and relaxation, making them a suitable strain sensor.

Dual Gold-Nanoslit Electrodes for Ultrasensitive Detection of Antigen-Antibody Reactions in Electrochemical Surface Plasmon Resonance

We present the use of surface charges in dual gold-nanoslit electrodes to improve the surface plasmon resonance (SPR) detection limit by several orders of magnitude. The SPR is directly generated by gold-nanoslit arrays in the two electrodes. The SPR shifts for both nanoslit arrays are measured simultaneously with a simple hyperspectral setup. When biomolecules are captured by specific antibodies on the dual electrodes, the surface charge is changed during the electrochemical process due to the increase in surface impedance. The push-pull-type electrodes generate opposite surface charges. Using the differences in both spectral shifts, the change in surface charge is detected sensitively. We demonstrate that using a [Fe(CN)₆]^3-/4- redox process after antigen-antibody interactions, the dual nanoslit electrodes show an enhancement of the detection limit from 1 μg/mL to 10 pg/mL.