Porous Silicon-Based Aptasensors: Toward Cancer Protein Biomarker Detection

Abstract

The anterior gradient homologue-2 (AGR2) protein is an attractive biomarker for various types of cancer. In pancreatic cancer, it is secreted to the pancreatic juice by premalignant lesions, which would be an ideal stage for diagnosis. Thus, designing assays for the sensitive detection of AGR2 would be highly valuable for the potential early diagnosis of pancreatic and other types of cancer. Herein, we present a biosensor for label-free AGR2 detection and investigate approaches for enhancing the aptasensor sensitivity by accelerating the target mass transfer rate and reducing the system noise. The biosensor is based on a nanostructured porous silicon thin film that is decorated with anti-AGR2 aptamers, where real-time monitoring of the reflectance changes enables the detection and quantification of AGR2, as well as the study of the diffusion and target-aptamer binding kinetics. The aptasensor is highly selective for AGR2 and can detect the protein in simulated pancreatic juice, where its concentration is outnumbered by orders of magnitude by numerous proteins. The aptasensor’s analytical performance is characterized with a linear detection range of 0.05–2 mg mL–1, an apparent dissociation constant of 21 ± 1 μM, and a limit of detection of 9.2 μg mL–1 (0.2 μM), which is attributed to mass transfer limitations. To improve the latter, we applied different strategies to increase the diffusion flux to and within the nanostructure, such as the application of isotachophoresis for the preconcentration of AGR2 on the aptasensor, mixing, or integration with microchannels. By combining these approaches with a new signal processing technique that employs Morlet wavelet filtering and phase analysis, we achieve a limit of detection of 15 nM without compromising the biosensor’s selectivity and specificity.

Gold Nanorod-Incorporated Halloysite Nanotubes Functionalized with Antibody for Superior Antibacterial Photothermal Treatment

“…Aminosilanization of the etched HNTs results in the addition of bands at 1564, 1487, and 1382 cm −1 associated with grafted surface amine and CH 2 deformation [ 45 , 47 , 49 ]. Following the reaction between the surface amine residues and the succinic anhydride, new bands are observed at 1632, 1552, and 1398 cm −1 , and are ascribed to the carbonyl residue in a newly formed amide bond and the stretching vibration of a carboxyl residue [ 45 , 50 ]. The spectrum of the reactive Sulfo-NHS intermediate includes two additional bands at 1789 and 1737 cm −1 , characteristic of cyclic imides [ 50 , 51 ].…”

Aptasensors versus immunosensors—Which will prevail?

“…Moreover, when surface-based aptasensors are considered, incorporation of a spacer to extend the binding region of the aptamer from the surface and minimize steric hindrance effects may also improve the aptamer functionality. The spacer can be a polyethylene glycol moiety fused with the aptamer sequence or on the surface, or by direct sequence elongation, such as the introduction of several thymine bases [102,103,109,111,[113][114][115]. The last aspect to be considered is preventing undesired electrostatic interactions between the negatively-charged aptamers and positively-charged surfaces, which may impede the aptamer's folding; this can be achieved via surface modification or passivation strategies [100,102].…”

“…Proper aptamer density on a surface is crucial for achieving sufficient binding sites for the target, while minimizing steric hindrance and electrostatic repulsion between neighboring aptamers. As such, aptamer immobilization onto nanomaterials and nanostructured surfaces, which are more prone to steric crowding effects, should be carefully designed [ 97 , 100 , 103 ‐ 105 ]. Furthermore, excessive density may also affect the analyte mass transfer rate, as was demonstrated for surface‐based biosensors [ 106 , 107 ].…”

“…This is dictated by the location of the terminus within the binding region of the aptamer and its involvement in the folding. Thus, both immobilization directions should be screened and compared for best results [ 100 , 102 , 103 , 111 , 113 ]. Moreover, when surface‐based aptasensors are considered, incorporation of a spacer to extend the binding region of the aptamer from the surface and minimize steric hindrance effects may also improve the aptamer functionality.…”

Silicon Nanostructures for Molecular Sensing: A Review

“…Further, Bandarenka et al presented a review on progressive developments in the fabrication and application of plasmonic NSs decorated on pSi for the application to the biochemical molecular SERS-based sensing. − This review highlights various plasmonic NSs like thin-film, nanovoids, nanoparticles, nanoarrays, and dendrites on the pSi surface. In this strategy, earlier in 2015, the Marin group continuously developed and dramatically explored AgNPs covered pSi for SERS-based trace level molecular detection .…”