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.