Rational engineering of synergically stabilized aptamer-cDNA duplex probes for strand displacement based electrochemical sensors

A novel dual-mode aptasensor based colorimetry and electrochemical detection of norovirus in fecal sample

Norovirus is a leading cause of acute gastroenteritis in humans. This paper presents the development of a novel dual-mode aptasensor for detecting norovirus using colorimetry and electrochemical methods. The initial colorimetric method utilizes gold nanoparticles (AuNPs) and sodium chloride to establish a positive correlation between the concentration of norovirus in a solution and the absorbance ratio A650/A520. The naked eye can detect concentrations as low as 0.1 μg/mL, corresponding to a Ct value of 33 (2.2 copies/μL, CT = 34.102-3.2185·lgX), allowing for qualitative and semi-quantitative analysis. For more accurate trace analysis, a gold electrode is modified with a thiol-modified aptamer and closed with 6-Mercapto-1-hexanol. After incubation with norovirus, the virus specifically binds to the aptamer, causing changes in its spatial structure and distance from the electrode surface. These changes can then be detected using electrochemical square wave voltammetry (SWV). Under optimal reaction conditions, the peak current from SWV exhibits a strong linear relationship with the logarithm of norovirus concentrations between 10-9 μg/mL and 10-2 μg/mL. The regression equation Y = 14.76789 + 1.03983·lgX, with an R2 value of 0.987, accurately represents this relationship. The limit of detection was determined to be 1.365 × 10-10 μg/mL. Furthermore, the aptasensor demonstrated high specificity for norovirus in fecal samples, making it a promising tool for detecting norovirus in various sample types.

High-sensitive ferrocene labeled aptasensor for the detection of Mucin 1 by tuning the sequence constitution of complementary probe

A strand displacement-based "signal-off" electrochemical aptasensor is reported for the detection of Mucin 1 (MUC 1) based on a high original signal. Different from the conventional "signal-off" electrochemical biosensors where electrochemical substances are dispersed in electrolyte solution, here the current signal was generated by the complementary probe (CP) associated with ferrocene (Fc) labeled aptamer (Apt.-Fc). Because Apt.-Fc and MUC 1 have a higher affinity, Apt.-Fc dissociates from CP in the presence of MUC 1, resulting in a reduction of detection current signal generated by oxidation of labeled Fc. In this system, high detection signal is necessary to improve the sensor's performance. For this aim, a strategy is proposed for changing the modalities of electron transport and the quantity of Apt.-Fc introduced by simply tuning the sequence constitution of CP. As expected, a high detection current signal was obtained after selecting CP(Apt.-Fc)-TTT as the optimal CP. The aptasensor was then employed to detect MUC 1, and satisfactory detection results with a low detection limit (LOD) of 0.087 pM (S/N = 3), good specificity, good stability, and feasibility of detection of MUC 1 in artificial serum (recovery of 92-101%, RSD of 1.36-5.23%) were obtained.

Electrochemical/visual dual-readout aptasensor for Ochratoxin A detection integrated into a miniaturized paper-based analytical device

Development of portable, sensitive and reliable devices for Ochratoxin A (OTA) detection is highly demanded, especially for resource-limited regions. Herein, a novel paper-based analytical device (PAD) is designed through wax printing and screen-printed technologies, which integrates sample flowing, electrode modification, cleaning and electrochemical (EC)/colorimetric signal output. To greatly enhance the detection sensitivity, we synthesized a chitosan functionalized MoS₂-Au@Pt (Ch-MoS₂-Au@Pt) via electrostatic self-assembly, and used it to immobilize the label aptamer (apta₂) for signal regulation and amplification. Concretely, with the addition of analytes, the Ch-MoS₂-Au@Pt-apta₂ could be combined on the sensing interface by specific biorecognition and catalyzed reduction of H₂O₂, resulting in a remarkable EC response. Meanwhile, the released hydroxyl radicals (·OH) flowed to the visualization zone and promoted the oxidation of 3,3',5,5'-tetramethylbenzidine for colorimetric detection. Consequently, the dual-mode PAD achieved acceptable prediction and accurate analysis in the range of 0.1-200 ng mL^-1 and 1 × 10^-4-200 ng mL^-1 by matching the visual and EC signal intensity, respectively. Compared with traditional single-mode sensor for OTA, the proposed dual-mode aptasensor featuring independent signal conversion and readout, not only avoided the false-positive signal associated with detection condition and operation, but also enlarged the detection ranges and improved the sensitivity. Furthermore, the consistency of EC/colorimetric assay was validated in real OTA samples. Overall, this work provided a portable, cost-effective, sensitive and visualized aptasensor platform, which could be extended to various other mycotoxins in the field of food safety.

Lengthening the aptamer to hybridize with a stem-loop DNA assistant probe for the electrochemical detection of kanamycin with improved sensitivity

By adding 6 thymines to lengthen the parent aptamer combined with the change of "on" and "off" induced by the target for an assistant stem-loop DNA probe (ASP-SLP-MB), a new folding-type electrochemical kanamycin (Kana) aptamer-engineering dual-probe-based sensor (sensor d) was developed. By purposefully reducing the background current and increasing the electron transfer efficiency of methylene blue (MB), the sensor obtained significantly enhanced detection sensitivity compared with non-aptamer-engineering one-probe-based sensor (sensor a). Such efficacy was validated by a big decrease from 530.6 to 210.2 nA for the background current signal and from 360 to 0.3 nM for the detection limit. In addition to the improved sensitivity, the sensor also exhibited good selectivity, anti-fouling detection performance, and potential quantitative analysis ability, showing a feasible potential practical analytical application in real-life complicated samples, for example, milk and serum. The released results prove that the aptamer-engineering method is effective in improving the analytical performance of folding-type sensors and provides a methodological guidance for the design and fabrication of other high-performance folding-type aptasensors. Graphical abstract.

Self-Polymerized Dopamine-Decorated Au NPs and Coordinated with Fe-MOF as a Dual Binding Sites and Dual Signal-Amplifying Electrochemical Aptasensor for the Detection of CEA

Fabrication of functional electrochemical biosensor is a hot topic; however, precise and sensitive cancer detection in early clinical diagnosis is still a great challenge. Continuous efforts have been devoted to explore functional materials for this issue. In this work, we developed a dual binding sites and dual signal-amplifying electrochemical aptasensor of self-polymerized dopamine-decorated Au and coordinated with Fe-MOF (Au@PDA@Fe-MOF) for the detection of carcinoembryonic antigen (CEA). Remarkably, Au@PDA@Fe-MOF features high sensitivity, multiple active sites, good biocompatibility, and excellent selectivity, which is attributed to abundant -COOH in porous Fe-MOF and unsaturated Fe³⁺ sites on the surface of Fe-MOF as the active binding sites grafting more NH₂-functionalized CEA-specific aptamer and redox PDA and Fe-MOF accelerating the movement of electrons for dual signal amplifying. Meanwhile, the electrochemical aptasensor shows favorable repeatability with 1.82% relative standard deviation (RSD) under five independent aptasensors and strong stability with only 3.3% degradation after 12 days of storage. In addition, the aptasensor has wide CEA detection range from 1 fg mL^-1 to 1 μg mL^-1 with a low detection limit of 0.33 fg mL^-1 (S/N = 3). Furthermore, the aptasensor is feasible for accurate and quantitative detection of CEA in serum samples with RSD below 2.32%. The satisfying results demonstrate promising applications of the CEA aptasensor in practical sample analysis and lay an important foundation for other biomarker detection in early clinical diagnosis.

A rapid and simple ratiometric fluorescent sensor for patulin detection based on a stabilized DNA duplex probe containing less amount of aptamer-involved base pairs

In this study, a sensor is described for determination of patulin by using ratiometric fluorescence measurement and strand displacement strategy. In the presence of patulin, the ratiometric fluorescence response decreases, owing to disassembly of DNA duplex structure and target-mediated release of TAMRA-labeled complementary DNA sequence2 (cDNA2). While, in the absence of target, the fluorescence resonance energy transfer (FRET) phenomenon happens between FAM and TAMRA under excitation at 490 nm, resulting in the enhancement of ratiometric signal. The use of ratiometric fluorescence signal with different signal indicators avoids the problem of environmental interference and improves the sensitivity of the aptasensor. Also, the DNA duplex structure contains minimum aptamer-involved base pair sequence, resulting in further improvement of the aptasensor sensitivity. This sensing platform provided a wide linear range from 15 ng/L to 35 μg/L and a detection limit of 6 ng/L for patulin. The aptasensor was used to determine patulin in spiked apple juice samples and showed satisfactory results.

Novel nanoarchitecture of Co-MOF-on-TPN-COF hybrid: Ultralowly sensitive bioplatform of electrochemical aptasensor toward ampicillin

Owning to the misuse of the antibiotics in animal husbandry and agriculture, it is highly urgent to determine the quantification of antibiotics in biological systems by the simple, sensitive, and fast method. In this work, a novel nanoarchitecture of Co-based metal-organic frameworks (Co-MOF) and terephthalonitrile-based covalent organic framework (TPN-COF) was synthesized (represented by Co-MOF@TPN-COF), followed by the exploitation as the bioplatform of non-label aptasensor for detecting the most frequently used β-lactam antibiotics, ampicillin (AMP). The new porous hybrid material of Co-MOF@TPN-COF was synthesized by adding the as-prepared TPN-COF into the Co-MOF preparation system. The multilayered Co-MOF@TPN-COF nanosheets exhibit a high specific surface area (52.64 m² g^-1), nitrogen-rich groups and excellent electrochemical activity. As a result, large amounts of aptamer strands can be bound over the Co-MOF@TPN-COF nanosheets owning to the strong π-π stacking and hydrogen bonds. When detecting AMP by the electrochemical impedance spectroscopy, the fabricated Co-MOF@TPN-COF-based aptasensor exhibits an ultra-low detection limit of 0.217 fg mL^-1 within the AMP concentration from 1.0 fg mL^-1 to 2.0 ng mL^-1, which was superior to those previously reported in literatures. In addition, this proposed aptasensor also shows high selectivity, good reproducibility and stability, acceptable regenerability, and favorable applicability in human serum, river water and milk. Therefore, the proposed Co-MOF@TPN-COF-based aptasensor has a great promise to be applied as a powerful tool in the fields of food safety.