Ascorbic Acid-Mediated in situ Growth of Gold Nanostars for Photothermal Immunoassay of Ochratoxin A

A photothermal aptasensor based on rolling circle amplification-enriched DNAzyme for portable detection of ochratoxin A in grape juice

Aptasensors for detection of ochratoxin A (OTA) have been extensively studied, but the majority of them require costly and large-scale equipment as signal readers. Herein, a photothermal aptasensor capable of portable detection of OTA through a thermometer was developed on basis of aptamer structural switching and rolling circle amplification (RCA)-enriched DNAzyme. Oligonucleotides and alkaline phosphatase (ALP) modified magnetic beads were prepared. The binding of aptamers to OTA led to the release of ALP labeled complementary DNA. After magnetic separation, ALP catalyzed the padlock dephosphorylation, inhibiting the subsequent RCA reaction. This process converted the OTA concentration into the amount of the photothermal reagent oxTMB produced from the catalytic reaction induced by RCA-enriched DNAzyme. Under the optimal conditions, the detection limit (LOD) of this aptasensor was 2.28 nM in a clean buffer, while the LOD reached 2.43 nM in 2 % grape juice. The good performance of the photothermal aptasensor makes it possible to measure OTA pollution in low resource environments.

Colorimetric and photothermal dual-mode aptasensor with redox cycling amplification for the detection of ochratoxin A in corn samples

Ochratoxin A (OTA) detection is critical for public health safety. This study proposes a G-quadruplex-Hemin/iodide (G4-Hemin/I-)-mediated non-enzyme redox cycling amplification (RCA) system for dual-modal (colorimetric and photothermal thermometer) OTA analysis. The proposed aptasensor platform for point-of-care testing employs a common thermometer for quantitative signal readouts. The OTA aptamer folds into a G4 structure, which significantly enhances the catalytic activity in the presence of I- after RCA reaction. Moreover, a notable temperature enhancement causes color changes, providing an ultrasensitive and label-free platform for OTA detection. Further, the designed sensor was applied to OTA content determination in corn samples and achieved satisfactory results compared to a commercial enzyme-linked immunoassay kit. The proposed dual-mode aptasensor is simple, highly sensitive (1 pg/mL for colorimetric method, 0.8 pg/mL for photothermal method), selective, and suitable for low-cost instrument-free bioanalysis in low-resource settings.

A facile dual-mode immunosensor based on speckle Ag-doped nanohybrids for ultrasensitive detection of Ochratoxin A

Ochratoxin A (OTA) is a potent carcinogen, and is among the most dangerous mycotoxins in agricultural products. In this study, an ultrasensitive dual-mode immunosensor was developed for naked-eye and fluorescence detection of OTA based on Ag-doped core-shell nanohybrids (Ag@CSNH). Complete antigen-labeled Ag@CSNH (CA-Ag@CSNH) were used as a competitive bind and dual-mode probe. The diffused doping structure of CA-Ag@CSNH provided improved stability, color and fluorescence quencher performance. Antibodies modified magnetic beads were used as a capture probe. The competitive binding between OTA and CA-Ag@CSNH produced both color change and fluorescence quenching. Ultraviolet and fluorescence intensitie correlated linearly with OTA concentration ranges of 0.03-3 ng/mL and 10-10000 pg/mL, and limits of detection of 0.0235 ng/mL and 0.9921 pg/mL, respectively. The practical applicability of proposed strategy was demonstrated by analysis of OTA in spiked corn, soybean and flour samples. This study offers a new insight on multi-mode platforms for various applications.