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In this work, a microfluidic paper-based fluorescent sensor device was constructed for quantitative detection of microRNA (miRNA) and determination of the expression of folate receptor (FR) on the cell surface. It is worth pointing out that simultaneous detection of two biomarkers in cancer was achieved through dynamic self-assembly of T-shaped duplex structure. T-shaped duplex structure can respond to specific triggers and convert to an output due to the conformation changes, it is meaningful to fabricate T-shaped duplex structure into powerful biosensors that can monitor chemical stimuli. Moreover, lamellar MnO 2 nanosheets were synthesized, which exhibited excellent quenching ability via adsorbed fluorophore-labeled ssDNA, but the adsorption of the dsDNA was significantly lower than ssDNA because of the shielding of nucleobase pairs by the phosphate groups. This newly designed biosensor provided a sensitive detection of miR-21 from 0.01 to 5.0 fM with a relatively low detection limit of 0.0033 fM. Besides, the present sensing system has a detection of FR in the range from 2.0 to 30.0 ng/mL with the detection limit of 0.667 ng/mL. As biological markers for disease diagnosis, the detection of FR and miRNA will provide a new approach and therapeutic tool for early clinical diagnosis. [ABSTRACT FROM AUTHOR]

This study is an investigation for an inexpensive, simple and sensitive biosensor to detect prostate cancer using bioactivated-multi wall carbon nanotubes (MWCNTs, diameter of 20 nm, length of 5 µm) and a micro-pore filter paper (pore size of 0.45 µm). For the immunoassay of prostate specific antigen (PSA), which is a biomarker of prostate cancer, MWCNTs were activated with PSA antibody (monoclonal antibody of the prostate specific antigen) by using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide sodium salt (NHSS). The activated MWCNTs were deposited on the micro-pore filter paper to use as a biosensor. The prepared biosensor can assay from 0 to 500 ng/mL of PSA level within 2 h with the detection limit of 1.18 ng/mL by the measurement of resistance change. The resistance change was caused by site selective interaction between PSA and PSA-antigen with an inexpensive bench top digital multimeter (5 1/2 digits). The detection range and sensitivity of the prepared sensor are good enough to diagnose the early stage of prostate cancer (> 4 ng/mL of PSA). This paper-based biosensor is about 20 times cheaper (fabricated biosensor price: 2.4 $) and over 10 times faster than enzyme-linked immunosorbent assay (ELISA), which is a general method for the detection of a specific protein in the modernized hospitals. Furthermore, the maximum detection limit is about 50 times higher than ELISA. [ABSTRACT FROM AUTHOR]

Abnormal expression of MicroRNA-21 (miRNA-21) is considered to be a reliable biomarker for the early diagnosis of cancer. In this work, a novel paper based biosensor was fabricated to detect sub-micro molar concentrations of miRNA-21 based on peroxidase mimetic activity of DNA-templated Ag/Pt nanoclusters (DNA-Ag/Pt NCs), which could catalyze the reaction of hydrogen peroxide and 3,3′,5,5′ tetramethylbenzidine (TMB), to produce a blue color. The Mechanism of reaction was based on the inhibition effect of miRNA-21 on peroxidase-like activity of nanosensor which resulted to quantitative determination of miRNA-21 concentration. It was found that miRNA-21 could be linearly detected in the range from 1-700 pM (A 652 = 0.16x-0.96, R2 = 0.99; x = -log [miRNA-21]) with a detection limit of 0.6 pM. Moreover, a paper assay was carried out on a Y-shaped paper-based microfluidic device in order to use the distinctive features of micro-channels such as short response time, very low reagent volume, low fabrication cost, etc. After performing paper based assay, a good linear range was observed between 10-1000 pM (y = 0.06x+147.48, R2 = 0.99; x = [miRNA-21]) with detection limit of 4.1 pM. The practical application of proposed method for detection of miRNA-21 in real sample was assayed in the human urine sample and indicated the colorimetric method had acceptable accuracy. Image 1 • A novel paper-based microfluidic sensor was designed for detection of miRNA-21. • The miRNA-21 detection mechanism is based on peroxidase mimetic activity of DNA-Ag/Pt NCs. • The color change was obvioused in different concentration of miRNA-21. • This strategy shows excellent selectivity toward miR-21. [ABSTRACT FROM AUTHOR]