A new electrochemical aptasensor based on a dual-signaling strategy and supersandwich assay

APTES-Modified Remote Self-Assembled DNA-Based Electrochemical Biosensor for Human Papillomavirus DNA Detection

High-risk human papillomavirus (HPV) infection is an important cause of cervical cancer formation; therefore, being able to detect high-risk HPV (e.g., HPV-16) is important for the early treatment and prevention of cervical cancer. In this study, a combination of a 3-aminopropyltriethoxysilane (APTES) modified gold electrode and a super sandwich structure was creatively developed, resulting in the development of a biosensor that is both sensitive and stable for the detection of HPV-16. The electrochemical biosensor possesses a lower detection limit compared with previous studies with an LOD of 5.475 × 10⁻¹⁶ mol/L and it possesses a wide linear range from 1.0 × 10⁻¹³ mol/L to 1.0 × 10⁻⁶ mol/L (R² = 0.9923) for the target DNA. The experimental data show that the sensor has good stability, and there is no significant decrease in the current response value after 7 days in the low-temperature environment. In addition, the sensor proved to be a powerful clinical tool for disease diagnosis because it showed good interference resistance in complex human serum samples.

Highly Selective and Sensitive microRNA-210 Assay Based on Dual-Signaling Electrochemical and Photocurrent-Polarity-Switching Strategies

Highly sensitive and selective microRNA (miRNA) assay is of great significance for disease diagnosis and therapy. Herein, a magnetic-assisted electrochemistry (EC)-photoelectrochemistry (PEC) dual-mode biosensing platform was developed for miRNA-210 detection based on dual-signaling EC and photocurrent-polarity-switching PEC strategies. Porous magnetic Fe₃O₄ octahedra with a large surface area were synthesized by calcining Fe-based metal-organic frameworks. Subsequently, the magnetic photoelectric materials (Fe₃O₄@CdS) were developed by the successive ionic layer adsorption and reaction method in Cd²⁺ and S^2- solutions. Then, the self-assembled DNA nanoprisms contained three thiols/hanging arms that could capture miRNA-210 efficiently and were anchored to the Fe₃O₄@CdS octahedra via the Cd-S bond. When miRNA-210 was present, the double-stranded DNA concatemers [the self-assembled duplex helixes based on a pair of methylene blue (MB)-labeled single-stranded DNAs (AP1 and AP2) through the hybridization chain reaction and then intercalated with adriamycin (Dox) into their grooves] were connected with the Fe₃O₄@CdS-DNA nanoprisms. MB and Dox not only acted as the electrochemical probes but also synergistically switched the photocurrent polarity of the Fe₃O₄@CdS octahedra. Thus, miRNA-210 was assayed sensitively and selectively via the proposed EC-PEC dual-mode biosensing platform. Additionally, the abovementioned recognition steps occurred in a homogeneous system, and the effects of the impurities and interferences on the miRNA-210 assay could be easily avoided by magnetic separation due to the good magnetic properties of Fe₃O₄ octahedra. The proposed EC-PEC dual-mode biosensing platform showed a wide range of potential applications in bioanalysis and early diagnosis of disease.

Ratiometric Electrochemistry: Improving the Robustness, Reproducibility and Reliability of Biosensors

Electrochemical biosensors are an increasingly attractive option for the development of a novel analyte detection method, especially when integration within a point-of-use device is the overall objective. In this context, accuracy and sensitivity are not compromised when working with opaque samples as the electrical readout signal can be directly read by a device without the need for any signal transduction. However, electrochemical detection can be susceptible to substantial signal drift and increased signal error. This is most apparent when analysing complex mixtures and when using small, single-use, screen-printed electrodes. Over recent years, analytical scientists have taken inspiration from self-referencing ratiometric fluorescence methods to counteract these problems and have begun to develop ratiometric electrochemical protocols to improve sensor accuracy and reliability. This review will provide coverage of key developments in ratiometric electrochemical (bio)sensors, highlighting innovative assay design, and the experiments performed that challenge assay robustness and reliability.

Aptamer superstructure-based electrochemical biosensor for sensitive detection of ATP in rat brain with in vivo microdialysis

Highly sensitive and selective sensing of ATP in rat brain has attracted increasing interest from interdisciplinary fields of analytical chemistry and neuroscience owing to the importance of ATP in cellular metabolism and signal transduction. Herein, we demonstrated an electrochemical biosensor having an aptamer superstructure as a recognition element for the selective and sensitive detection of ATP in rat brain. Unlike the electrochemical aptamer-based sensors (aptasensors) built by assembling a simple DNA structure containing only one aptamer unit onto the electrode substrate, the aptasensor described here was developed by assembling an aptamer superstructure consisting of consecutive aptamer units in DNA strands onto the electrode substrate. Each aptamer unit in the superstructure was labelled with an electrochemical probe (i.e., methylene blue, MB) for signal readout. The aptamer superstructure was assembled onto the surface of a gold electrode to form the electrochemical aptasensor. In the presence of ATP, the strong electrochemical signals produced by multiple redox molecules labeled on the aptamer units clearly decreased because of the disassembling of the aptamer superstructure from the electrode surface due to strong interactions between ATP and the aptamer units. In this approach, the aptasensor was well responsive to the ATP concentration, and the current decrease was linearly related to the ATP concentration ranging from 0.1 nM to 1 mM. Moreover, the aptasensor has high selectivity and good regenerability. Due to these properties, the aptasensor with an aptamer superstructure can exhibit practical applications for ATP assay in rat brain combined with in vivo microdialysis.

An isothermal electrochemical biosensor for the sensitive detection of microRNA based on a catalytic hairpin assembly and supersandwich amplification

A novel isothermal electrochemical biosensor was proposed for the sensitive detection of microRNA (miRNA) based on the ingenious combination of the target-catalyzed hairpin assembly (CHA) and supersandwich amplification strategies. Since miRNA-221 has been reported to be overexpressed in cancers and has been a potentially useful biomarker for the diagnosis of the related diseases, miRNA-221 was chosen as a model target miRNA. The target miRNA-221 triggered a toehold strand displacement assembly of the two hairpin substrates, which led to the cyclicality of the target miRNA and the CHA products. Subsequently, the CHA products hybridized with a capture probe on the electrode and the exposed stem of the CHA products was further used to propagate the supersandwich. After this, the signal probe was modified with horseradish peroxidase (HRP) to form a supersandwich multiplex HRP-DNA label, which could achieve an amplified electrochemical signal. Using the isothermal dual signal amplification strategies, miRNA-221 as low as 0.6 pM (3σ) could be detected. In addition, this biosensor showed high selectivity and could discriminate miRNA-221 from the homologous miRNAs. Note that human miRNA from cancer cells could also be detected and the results were in excellent agreement with those obtained using qRT-PCR. Given that the biosensor avoided the introduction of nanoparticles, the limitation of using the nanoparticles was overcome. The proposed biosensor has great potential for broad applications in the field of clinical analysis.

Engineering Biosensors with Dual Programmable Dynamic Ranges

Although extensively used in all fields of chemistry, molecular recognition still suffers from a significant limitation: host-guest binding displays a fixed, hyperbolic dose-response curve, which limits its usefulness in many applications. Here we take advantage of the high programmability of DNA chemistry and propose a universal strategy to engineer biorecognition-based sensors with dual programmable dynamic ranges. Using DNA aptamers as our model recognition element and electrochemistry as our readout signal, we first designed a dual signaling "signal-on" and "signal-off" adenosine triphosphate (ATP) sensor composed of a ferrocene-labeled ATP aptamer in complex to a complementary, electrode-bound, methylene-blue labeled DNA. Using this simple "dimeric" sensor, we show that we can easily (1) tune the dynamic range of this dual-signaling sensor through base mutations on the electrode-bound DNA, (2) extend the dynamic range of this sensor by 2 orders of magnitude by using a combination of electrode-bound strands with varying affinity for the aptamers, (3) create an ultrasensitive dual signaling sensor by employing a sequestration strategy in which a nonsignaling, high affinity "depletant" DNA aptamer is added to the sensor surface, and (4) engineer a sensor that simultaneously provides extended and ultrasensitive readouts. These strategies, applicable to a wide range of biosensors and chemical systems, should broaden the application of molecular recognition in various fields of chemistry.

Ratiometric electrochemical detection of hydrogen peroxide and glucose

Hydrogen peroxide (H₂O₂) detection is of high importance as it is a versatile (bio)marker whose detection can indicate the presence of explosives, enzyme activity and cell signalling pathways. Herein, we demonstrate the rapid and accurate ratiometric electrochemical detection of H₂O₂ using disposable screen-printed electrodes through a reaction-based indicator assay. Ferrocene derivatives equipped with self-immolative linkers and boronic acid ester moieties were synthesised and tested, and, through a thorough assay optimisation, the optimum probe showed good stability, sensitivity and selectivity towards H₂O₂. The optimised conditions were then applied to the indirect detection of glucose via an enzymatic assay, capable of distinguishing 10 μM from the background within minutes.

Hybridization chain reaction-based colorimetric aptasensor of adenosine 5'-triphosphate on unmodified gold nanoparticles and two label-free hairpin probes

This work designs a new label-free aptasensor for the colorimetric determination of small molecules (adenosine 5'-triphosphate, ATP) by using visible gold nanoparticles as the signal-generation tags, based on target-triggered hybridization chain reaction (HCR) between two hairpin DNA probes. The assay is carried out referring to the change in the color/absorbance by salt-induced aggregation of gold nanoparticles after the interaction with hairpins, gold nanoparticles and ATP. To construct such an assay system, two hairpin DNA probes with a short single-stranded DNA at the sticky end are utilized for interaction with gold nanoparticles. In the absence of target ATP, the hairpin DNA probes can prevent gold nanoparticles from the salt-induced aggregation through the interaction of the single-stranded DNA at the sticky end with gold nanoparticles. Upon target ATP introduction, the aptamer-based hairpin probe is opened to expose a new sticky end for the strand-displacement reaction with another complementary hairpin, thus resulting in the decreasing single-stranded DNA because of the consumption of hairpins. In this case, gold nanoparticles are uncovered owing to the formation of double-stranded DNA, which causes their aggregation upon addition of the salt, thereby leading to the change in the red-to-blue color. Under the optimal conditions, the HCR-based colorimetric assay presents good visible color or absorbance responses for the determination of target ATP at a concentration as low as 1.0nM. Importantly, the methodology can be further extended to quantitatively or qualitatively monitor other small molecules or biotoxins by changing the sequence of the corresponding aptamer.