Porous Silicon-Based Aptasensors: Toward Cancer Protein Biomarker Detection

The anterior gradienthomologue-2 (AGR2) protein is an attractivebiomarker for various types of cancer. In pancreatic cancer, it issecreted to the pancreatic juice by premalignant lesions, which wouldbe an ideal stage for diagnosis. Thus, designing assays for the sensitivedetection of AGR2 would be highly valuable for the potential earlydiagnosis of pancreatic and other types of cancer. Herein, we presenta biosensor for label-free AGR2 detection and investigate approachesfor enhancing the aptasensor sensitivity by accelerating the targetmass transfer rate and reducing the system noise. The biosensor isbased on a nanostructured porous silicon thin film that is decoratedwith anti-AGR2 aptamers, where real-time monitoring of the reflectancechanges enables the detection and quantification of AGR2, as wellas the study of the diffusion and target-aptamer binding kinetics.The aptasensor is highly selective for AGR2 and can detect the proteinin simulated pancreatic juice, where its concentration is outnumberedby orders of magnitude by numerous proteins. The aptasensor'sanalytical performance is characterized with a linear detection rangeof 0.05-2 mg mL(-1), an apparent dissociationconstant of 21 & PLUSMN; 1 & mu;M, and a limit of detection of 9.2 & mu;g mL(-1) (0.2 & mu;M), which is attributedto mass transfer limitations. To improve the latter, we applied differentstrategies to increase the diffusion flux to and within the nanostructure,such as the application of isotachophoresis for the preconcentrationof AGR2 on the aptasensor, mixing, or integration with microchannels.By combining these approaches with a new signal processing techniquethat employs Morlet wavelet filtering and phase analysis, we achievea limit of detection of 15 nM without compromising the biosensor'sselectivity and specificity.