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Alkaline phosphatase (ALP), an extraordinary enzyme, can catalyze the dephosphorylation of small molecules, proteins and nucleic acids. ALP has been confirmed as a crucial serum diagnostic indicator, since the abnormal level of ALP is closely related to a variety of pathological processes, especially in the early diagnosis and screening of cancer. Herein, we designed a "turn-on" sensor to detect ALP and ascorbic acid (AA) based on the redox reaction between manganese dioxide (MnO2) coated upconversion nanoparticles (UCNPs) and AA. Firstly, 2 nm sized NaYF4:Yb3+,Tm3+ UCNPs were synthesized by a facile one-pot hydrothermal method. Then MnO2 coated UCNPs were prepared via electrostatic interactions between MnO2 nanosheets and UCNPs. MnO2 nanosheets could absorb blue light emitted by UCNPs near 471 nm under laser excitation at 980 nm, and so the luminescence of UCNPs was quenched based on luminescence energy transfer (LET). In the presence of AA, the luminescence was recovered again by the redox reaction between AA and MnO2 coated UCNPs. MnO2 nanosheets were reduced to Mn2+ and UCNPs were released. Furthermore, the "turn-on" sensor was applied to monitor ALP since the phosphate group of 2-phospho- L -ascorbic acid (AAP) was removed by ALP to yield AA. The bio-assay showed a good linear relationship between the restored luminescence intensities (ΔI = I − I0) and ALP concentrations ranging from 0.25 to 150 mU mL−1 with a limit of detection (LOD) of 0.045 mU mL−1 and between ΔI and AA concentrations ranging from 0.5 to 250 μM with an LOD of 0.29 μM. The luminescent sensor was also successfully applied for detection of ALP and AA in human serum samples with recoveries from 94.9% to 104.6% and 99.4% to 104.9%. [ABSTRACT FROM AUTHOR]

An ultra-high sensitivity sensor with the function of chiral signal amplification has been proposed for the enantiomer discrimination of various amino acid enantiomers based on charge transfer (CT)-induced SERS spectroscopy. The introduced TiO2 in this sensor improves the CT behavior and discrimination efficiency distinctly and enantiomeric discrimination is realized even at low concentration. [ABSTRACT FROM AUTHOR]

We proposed a novel readout method based on a peculiar phenomenon in which the vibrational frequencies of a SERS-active probe (dimethyldithiocarbamic acid sodium salt, DASS) can be affected when there is mercury species. Compared to the SERS intensity-dependent quantitative determination method, SERS frequency-shift-based methods have several advantages: smaller standard deviation, perfect linear relationship, and higher accuracy and sensitivity. In addition, the SERS frequency-shift-based method was not affected by irreproducible aggregation of the SERS substrate and instrumental factors, which greatly improved the application prospect of SERS-based detection. The DASS-modified silver nanoparticles produced a highly sensitive sensor specific to mercury species. Upon the addition of a solution of mercury species to the chip, the mercury species specifically binds to the sulfur atoms, which induces a frequency shift of the band at 1374 cm−1. The detection limit of the proposed method for Hg2+ is as low as 10−8 M. In addition, the proposed method exhibited the same phenomenon for organic mercury. Moreover, these results suggest that the proposed platform possesses the potential for sensitive, selective, and high-throughput on-site mercury pollution monitoring in resource-constrained settings. [ABSTRACT FROM AUTHOR]