ABSTRACT
The currently established DNA nanoprobes for the detection of mycotoxin from beverages have been limited by complicated sample pretreatment and uncontrollable nanoparticle flocculation in complex systems. We develop a rapid colorimetric approach for ochratoxin A (OTA) detection in Baijiu in a sample-in/"yes" or "no" answer-out fashion through target-modulated base pair stacking assembly of DNA-functionalized gold nanoparticles (DNA-AuNPs). The colorimetric signification of OTA relies on the competition of OTA with the AuNP surface-grafted DNA in binding with an OTA-targeted aptamer. The specific recognition of OTA by the aptamer prevents DNA duplex formation on the AuNP surface, thereby inhibiting the base pair stacking assembly of the DNA-AuNPs and giving rise to a "turn-on" color. By further suppressing DNA hybridization using a bulged loop design and an alcohol solution, the DNA-AuNPs exhibit an improved reproducibility for OTA sensing while maintaining excellent susceptivity to OTA. A detection limit of 88 nM was achieved along with high specificity towards OTA, which is lower than the maximum tolerated level of OTA in foodstuffs defined by countries worldwide. The entire reaction time, avoiding sample pretreatment, is less than 17 min. The DNA-AuNPs with anti-interference features and sensitive "turn-on" performance promise convenient on-site detection of mycotoxin from daily beverages.
Subject(s)
Aptamers, Nucleotide , Biosensing Techniques , Metal Nanoparticles , Mycotoxins , Ochratoxins , Gold , Base Pairing , Reproducibility of Results , Ochratoxins/analysis , DNA/genetics , Limit of DetectionABSTRACT
Test strips represent a class of point-of-care testing (POCT) tools for analysis of a variety of biomarkers towards diagnostics. Conventional test strips offer benefits of simple operation, visualization, and short detection time, along with the drawbacks of relatively low sensitivity and unavailability of quantitative analysis. Recently, the combination of surface-enhanced Raman scattering (SERS) and test strips have evolved to provide a powerful platform capable of ultrasensitive and multiplex detection of extensive analytes of interest. In this review, we focus on the working principles, design strategies and POCT applications of SERS-based test strips. Initially, both lateral and vertical flow test strips are briefly introduced, followed by presentation of various strategies for reforming SERS-based test strips with better detection performance. Applications of SERS-based test strips in diagnosis of disease biomarkers, nucleic acids and toxins are reviewed, with an emphasis on SERS tag design, sensitivity and analytical applicability. Finally, conclusions are made and perspectives on futuristic research directions are given.
Subject(s)
Biosensing Techniques , Metal Nanoparticles , Biomarkers , Point-of-Care Testing , Spectrum Analysis, RamanABSTRACT
Strains in biomolecules greatly restrict their structural flexibility. The effects of DNA's structural flexibility on nanoparticle stability have remained less explored in the field of plasmonic biosensors. In the present study, we discover the opposite effects of a rigid loop and a flexible single-stranded DNA (ssDNA) region in DNAzyme on the colloidal stability of gold nanoparticles (AuNPs), which afford "turn-on" plasmonic detection of Pb2+. In specific, DNAzyme-functionalized AuNPs undergo spontaneous assembly at high ionic strength upon hybridization to their substrate sequence because of a DNA base stacking interaction. In the presence of Pb2+, however, the DNAzyme grafted on the AuNP cleaves the substrate and forms an ssDNA region in the middle of the rigid loop. The induced structural flexibility of the surface-grafted DNAzyme by the ssDNA region in the middle helps elevate interparticle entropic repulsion, thereby bringing AuNP assemblies back to dispersion. We discover that this process can afford a dramatic increase of the AuNPs' plasmon resonance for determination of Pb2+ concentration. Under optimized conditions, a detection limit of 8.0 nM can be achieved for Pb2+ by this method with high selectivity. Its applicability to Pb2+ analysis in tap water samples has also been demonstrated.
