Research progress on nanomaterial-based matrices for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis.

Matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a novel soft ionization bio-mass spectrometry technology emerging in the 1980s, which can realize rapid detection of non-volatile, highly polar, and thermally unstable macromolecules. However, the analysis of small molecular compounds has been a major problem for MALDI-TOF MS all the time. In the MALDI analysis process based on traditional matrices, large numbers of interference peaks in the low molecular weight area and "sweet spots" phenomenon are produced, so the detection method needs to be further optimized. The promotion of matrix means the improvement of MALDI performance. In recent years, many new nanomaterial-based matrices have been successfully applied to the analysis of small molecular compounds, which makes MALDI applicable to a wider range of detection and useful in more fields such as pharmacy and environmental science. In this paper, the newly developed MALDI matrix categories in recent years are reviewed initially. Meanwhile, the potential applications, advantages and disadvantages of various matrices are analyzed. Finally, the future development prospects of nanomaterial-based matrices are also prospected.

Plasmonic Enhanced Gold Nanoclusters-Based Photoelectrochemical Biosensor for Sensitive Alkaline Phosphatase Activity Analysis.

Low-toxicity gold nanoclusters-decorated Ag@SiO2 (Au NCs-Ag@SiO2) nanocomposites modified plasmonic photoelectrodes were first fabricated to improve the photoelectric properties of Au NCs and practical application in biological detection. Through adjusting distance between Au NCs and plasmonic silver nanoparticles (Ag NPs), the photocurrent intensity of Au NCs enhanced by 3.8 times attributed to strong competition between enhancement functions of hot electron transfer, local electric field, light scattering effects, and quenching functions of nonradiative energy transfer. Further comparison between experimental results and theoretical simulations were conducted to gain a deeper understanding toward the photoelectric enhancement mechanism. Moreover, Au NCs-Ag@SiO2 nanocomposites was successfully applied to the construction of photoelectrochemical (PEC) biosensors for sensitively detecting alkaline phosphatase activity. This proposed PEC biosensor showed a wide linear range from 0.04 to 400 U·L-1, and a low detection limit of 0.022 U·L-1.

Ratiometric fluorescent nanosensors for ultra-sensitive detection of mercury ions based on AuNCs/MOFs.

Ratiometric fluorescent nanosensors were developed to detect mercury ions (Hg2+) using enhanced dual emissions from glutathione stabilized gold nanoclusters/indium-based metal-organic frameworks modified with cysteine (AuNCs/MIL-68(In)-NH2/Cys). The nanosensors exhibited bright pink fluorescence with AuNCs evenly distributed on MIL-68(In)-NH2. Under 370 nm excitation, the obtained sensor presented double fluorescence emission around 438 nm and 668 nm, which was attributed to MIL-68(In)-NH2 and GSH-AuNCs, respectively. The fluorescence emission was remarkably enhanced after modification with Cys. In the presence of Hg2+, the red fluorescence peak at 668 nm was quenched, while the blue fluorescence peak at 438 nm was slightly altered. The prepared AuNCs/MIL-68(In)-NH2/Cys nanosensors exhibited two linear ranges for the detection of Hg2+, namely from 20 pM to 0.2 µM and 0.2 µM to 60 µM, with a detection limit of 6.7 pM. They also presented high selectivity towards other ions and good performance in real water samples. Moreover, a radial star-shaped microfluidic paper-based analytical device (µPAD), as a straightforward and convenient platform, was successfully fabricated for the visual detection of Hg2+ with a wide detection range from 5 nM to 50 µM.