Fluorometric determination of the activity of alkaline phosphatase based on a system composed of WS2 quantum dots and MnO2 nanosheets

Microwave-Assisted Synthesis of Sulfur Quantum Dots for Detection of Alkaline Phosphatase Activity

Sulfur quantum dots (SQDs) are a kind of pure elemental quantum dots, which are considered as potential green nanomaterials because they do not contain heavy metal elements and are friendly to biology and environment. In this paper, SQDs with size around 2 nm were synthesized by a microwave-assisted method using sulfur powder as precursor. The SQDs had the highest emission under the excitation of 380 nm and emit blue fluorescence at 470 nm. In addition, the SQDs had good water solubility and stability. Based on the synthesized SQDs, a fluorescence assay for detection of alkaline phosphatase (ALP) was reported. The fluorescence of the SQDs was initially quenched by Cr (VI). In the presence of ALP, ALP-catalyzed hydrolysis of 2-phospho-L-ascorbic acid to generate ascorbic acid. The generated ascorbic acid can reduce Cr (VI) to Cr (III), thus the fluorescence intensity of SQDs was restored. The assay has good sensitivity and selectivity and was applied to the detection of ALP in serum samples. The interesting properties of SQDs can find a wide range of applications in different sensing and imaging areas.

Portable smartphone device-based multi-signal sensing system for on-site and visual determination of alkaline phosphatase in human serum

To provide the basis for clinical diagnosis in an emergency case, a portable smartphone device-based multi-signal sensing system for on-site determination of alkaline phosphatase (ALP) is introduced. In this system, cobalt hydroxide (CoOOH) nanoflakes can oxidize O-phenylenediamine (OPD) to produce 2,3-diaminophenazine (OxOPD), resulting in a strong fluorescence at 565 nm and an absorbance at 420 nm, respectively. The ascorbic acid 2-phosphate (AAP) can be hydrolyzed by alkaline phosphatase (ALP) to yield ascorbic acid (AA). Then, AA reduces the CoOOH nanoflakes to produce Co²⁺, and AA is oxidized to form dehydroascorbic acid (DHAA), thereby inhibiting the formation of OxOPD. The reaction product DHAA further combines with OPD to yield 3-(1,2-dihydroxyethyl)furo[3,4-b]quinoxalin-1(3H)-one (DFQ) accompanied by a strong fluorescence at 430 nm. Based on this, the fluorometric assay for ALP has a wide linear range from 0.8 to 190 U/L with a low detection limit of 0.16 U/L, and the colorimetric assay from 3 to 130 U/L with a detection limit of 1.94 U/L. Moreover, a portable smartphone sensing platform integrated with fluorescent and colorimetric signals was established for rapid determination of ALP without spectrometers. Recoveries of 97-104% for spiked samples and relative standard deviations (RSD) of less than 2% (n = 3) confirmed the feasibility of the developed platform in complicated samples, opening up new horizons for on-site evaluation in the biomedical field.