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A label-free and selective aptamer beacon-based Love-wave biosensing device was developed for prostate specific antigen (PSA) detection. The device consists of the following parts: LiTaO3 substrate with SiO2 film as wave guide layer, two set of inter-digital transducers (IDT), gold film for immobilization of the biorecongniton layer and a polydimethylsiloxane (PDMS) microfluidic channels. DNA aptamer, or “artificial antibody”, was used as the specific biorecognition probe for PSA capture. Some nucleotides were added to the 3'-end of the aptamer to form a duplex with the 3'-end, turning the aptamer into an aptamer-beacon. Taking advantage of the selective target-induced assembly changes arising from the “aptamer beacon”, highly selective and specific detection of PSA was achieved. Furthermore, PDMS microfluidic channels were designed and fabricated to realize automated quantitative sample injection. After optimization of the experimental conditions, the established device showed good performance for PSA detection between 10 ng/mL to 1 μg/mL, with a detection limit of 10 ng/mL. The proposed sensor might be a promising alternative for point of care diagnostics.

Electrochemical DNA (E-DNA) sensors have been greatly developed and play an important role in early diagnosis of different diseases. To determine the extremely low abundance of DNA biomarkers in clinical samples, scientists are making unremitting efforts toward achieving highly sensitive and selective E-DNA sensors. Here, a novel E-DNA sensor was developed taking advantage of the signal amplification efficiency of nanoprobe-initiated enzymatic polymerization (NIEP). In the NIEP based E-DNA sensor, the capture probe DNA was thiolated at its 3'-terminal to be immobilized onto gold electrode, and the nanoprobe was fabricated by 5'-thiol-terminated signal probe DNA conjugated gold nanoparticles (AuNPs). Both of the probes could simultaneously hybridize with the target DNA to form a "sandwich" structure followed by the terminal deoxynucleotidyl transferase (TdT)-catalyzed elongation of the free 3'-terminal of DNA on the nanoprobe. During the DNA elongation, biotin labels were incorporated into the NIEP-generated long single-stranded DNA (ssDNA) tentacles, leading to specific binding of avidin modified horseradish peroxidase (Av-HRP). Since there are hundreds of DNA probes on the nanoprobe, one hybridization event would generate hundreds of long ssDNA tentacles, resulting in tens of thousands of HRP catalyzed reduction of hydrogen peroxide and sharply increasing electrochemical signals. By employing nanoprobe and TdT, it is demonstrated that the NIEP amplified E-DNA sensor has a detection limit of 10 fM and excellent differentiation ability for even single-base mismatch.

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Coupled with the ability of fast and quantitative response, electrochemical aptasensors (EA) have great potential in the application of early diagnosis of cancer biomarker. In order to determine the rare biomarkers in the complicate clinical samples, scientists are making unremitting efforts towards improving the sensitivity and selectivity of EA. Herein, a "sandwich"-structure electrochemical aptasensor (SEA) is developed for analysis of cancer biomarker carcino-embryonic antigen (CEA). Two DNA aptamers are employed, one of which is thiolated at 3'-terminal and immobilized onto the gold electrode as a capture probe, while the other one is served as signal probe. The two aptamers could "sandwich" the target and signal probe is then subjected to the terminal deoxynucleotidyl transferase (TdT)-catalyzed incorporation of biotin labeled dNTPs into its 3'-terminal. Thus the as-generated long DNA oligo tails allow specific binding of numerous avidin modified horseradish peroxidase (Av-HRP), resulting in enhanced peroxidase catalyzed electrochemical signals. This signal amplification strategy is termed as surface initiated enzymatic polymerization (SIEP). This SIEP amplified SEA has a detection limit of 10 pg•mL 1 , indicating the outstanding amplification efficiency.