Three-in-one via syringe needle-based device: sampling, microextraction and peroxidase-like catalysis for colorimetric detection of the change of biogenic amines levels with time in meat.

In this work, a syringe needle-based integrated method was designed for the detection of biogenic amines (BAs) in raw meat samples. Based on a sequential process, the needle-based sampling, micro liquid-phase extraction and peroxidase-like catalysis were adopted for the sample collection, target analytes extraction and colorimetric analysis, respectively. The proposed method exhibited high selectivity towards BAs (the total amount of histamine, putrescine and cadaverine was utilized to present the level of BAs), where the linear range is 5-50 µM and 50-1000 µM, and the limit of detection is 1.52 µM. Specifically, the whole process could be completed in a single syringe needle. In addition, due to the minimized sampling, the change of BAs levels with time in different area of real samples (fish) can be conveniently investigated. This method has the advantages of simplicity, low cost, high sensitivity and selectivity, endowing it a promising candidate for food analysis.

Gold nanoprism/Tollens' reagent complex as plasmonic sensor in headspace single-drop microextraction for colorimetric detection of formaldehyde in food samples using smartphone readout.

In this work, an assay with high sensitivity and selectivity for the detection of formaldehyde (FA) is presented. The assay applied a gold nanoprism/Tollens' reagent (Au-np/TR) complex as the sensor used in headspace single-drop microextraction (HS-SDME). A surface plasmon resonance signal enhancement as well as color change was caused by the formation of Au@Ag-np after a redox reaction between FA and TR during the HS-SDME process. With the utilization of smartphone nanocolorimetry (SNC), the FA could be detected and quantified. For HS-SDME-SNC, a linearity calibration curve ranging from 0.1 to 100 µM was obtained, and the limit of detection was determined to be 30 nM. Successful attempts to determine FA were demonstrated by analysis of the analyte in (adulterated) raw food samples (octopus and chicken flesh). Matrix effects from real samples were avoided by using HS-SDME, and only a 3-µL droplet of solvent was needed in the assay.

Smartphone Nanocolorimetric Determination of Hydrogen Sulfide in Biosamples after Silver-Gold Core-Shell Nanoprism-Based Headspace Single-Drop Microextraction.

In this work, the sensitive detection of hydrogen sulfide (H2S) was realized at low cost and high efficiency through the application of silver-gold core-shell nanoprism (Ag@Au-np) combined with headspace single-drop microextraction (HS-SDME). After SDME, smartphone nanocolorimetry (SNC), with the aid of a smartphone camera and color picker software, was used to detect and quantify the H2S. The method took advantage of the inhibition of the ultraviolet-visible (UV-vis) signal caused by H2S etching of the Ag@Au-np preadded to the SDME solvent to measure the H2S concentration. The coating of the gold layer not only ensured the high stability of the nanomaterial but also enhanced the selectivity toward H2S. The HS-SDME method was simple to process and required only a droplet of solvent for analysis to be realized. This HS-SDME-SCN approach exhibited a calibration graph linearity of between 0.1 and 100 µM and a limit of detection of 65 nM (relative standard deviations of N% ( n = 3) < 4.80). A comparison with UV-vis spectrophotometry was conducted. The practical applicability of HS-SDME-SNC was successfully demonstrated by determining H2S in genuine biosamples (egg and milk).