A signal-on photoelectrochemical aptasensor based on ferrocene labeled triple helix DNA molecular switch for detection of antibiotic amoxicillin

A sensitive signal-on photoelectrochemical aptasensor for antibiotic determination was constructed based on the energy level matching between ferrocene and CuInS2. P-type CuInS2 microflower was complexed with reduced graphene oxide (CuInS2/rGO) to get photocathode current with good photoelectric conversion efficiency and stability. Then, hairpin DNA (HP) was covalently bonded to the electrode surface. A triple helix DNA (THMS) was used as a molecular switch. After the specific recognition between target and THMS in homogeneous solution, ferrocene labeled probe (Fc-T2) was released. Finally, Fc-T2 was captured by the HP, which leaded the obvious increase of photocurrent for the energy level matching between ferrocene and CuInS2. The increase of the photocurrent signal was proportional to the concentration of target amoxicillin (AMOX), the linear range was 100 fM-100 nM with detection limit of 19.57 fM. Meanwhile, the method has been successfully applied for milk and lake water samples analysis with satisfactory results.

A dual-model immobilization-free photoelectrochemical/visual colorimetric bioanalysis based on microemulsion self-assemblies mediated multifunctional signal amplification strategy

Herein, a novel silver ion-loaded gold microemulsion assemblies (Au/Ag+ MAs) mediated multifunctional signal amplification strategy was proposed to construct a sensitive immobilization-free photoelectrochemical (PEC)/colorimetric biosensor for carcinoembryonic antigen (CEA) detection. Through the sandwiched reaction among CEA, the CEA aptamer (DNA1) loaded on the Au nanoparticles (NPs) functionalized iron oxide (Fe3O4) nanospheres and another CEA aptamer (DNA2) immobilized on Au/Ag+ MAs, a complex is formed and acquired by magnetic separation. Then, Au/Ag+ MAs of the complex are disassembled into Au NPs and Ag+ ions driven by an acetone response, and the obtained demulsification solution is transferred to the cadmium sulfide/cadmium telluride (CdS/CdTe) photoactive composites modified electrode. Based on the multiple inhibition functions (blocking effect of oleylamine; energy transfer effect of Au NPs; and electron snatching effect of Ag+), the photocurrent of the electrode decreases obviously, resulting in the ultrasensitive detection of CEA (a detection limit of 16 fg mL-1). Interestingly, the ion-exchange reactions between CdS/CdTe composites and Ag+ ions generate silver sulfide/silver telluride (Ag2S/Ag2Te) composites, and a color change of composites can be distinguished directly, leading to a quick visual detection of CEA. Compared with the traditional single-modal assay for CEA, such dual-modal PEC/colorimetric assay is a more accurate and reliable due to different mechanisms and independent signal conversion. This work will offer a new perspective for the applications of various self-assemblies in PEC bioanalysis.

A Direct-Contact Photocurrent-Direction-Switching Biosensing Platform Based on In Situ Formation of CN QDs/TiO2 Nanodiscs and Double-Supported 3D DNA Walking Amplification

Herein, a direct-contact photocurrent-direction-switching photoelectrochemical (PEC) biosensing platform for the ultrasensitive and selective detection of soluble CD146 (sCD146) is reported for the first time via in situ formation of carbon nitride quantum dots (CN QDs)/titanium dioxide (TiO2 ) nanodiscs with the double-supported 3D DNA walking amplification. In this platform, metal organic frameworks (MOFs)-derived porous TiO2 nanodiscs exhibit excellent anodic photocurrent, whereas a single-stranded auxiliary DNA (ssDNA) as biogate is absorbed onto the TiO2 nanodiscs to block active sites. Subsequently, with the help of intermediate DNAs from target sCD146-induced double-supported 3D DNA walking signal amplification, the ssDNA can leave away from the surface of TiO2 nanodiscs due to the specific hybridization with intermediate DNAs. Afterward, the successful direct contact of CN QDs on TiO2 nanodiscs by porosity and electrostatic adsorption, leads to the effective photocurrent-direction switching from anodic to cathodic photocurrent. Based on direct-contact photocurrent-direction-switching CN QDs/TiO2 nanodiscs system and double-supported 3D DNA walking signal amplification, sCD146 is detected sensitively with a wide linear range (10 fg mL-1 to 5 ng mL-1 ) and a low limit of detection (2.1 fg mL-1 ). Also, the environmentally friendly and direct-contact photocurrent-direction-switching PEC biosensor has an application prospect for cancer biomarker detection.

Multiorbital DNA walker nanoprobe for portable photothermal detection based on H2S etching of cubic Prussian blue

In the developed assay, multiorbital 3D DNA walker (MO DNA walker) was applied as signal amplified protocol for enhancing the detection signal of the photothermal biosensor, which was designed for sensitive detection of miRNA based on the H2S triggered conversation of photothermal reagent. When the target molecule is present, the DNA walking strand was released and then hybridize with track strands. The landing of walking particles (WPT) on the tracking particles (TPT) promotes the relative movement of the WPT around TPT, thus releasing large amount of horseradish peroxidase (HRP) with the aid of DNAzyme. After reacting with Na2S2O3 and H2O2, multiple H2S can be generated in situ based on the catalytic ability of HRP. Meanwhile, cubic Prussian blue (CPB) was synthesized and exhibited superior photothermal response, which can be served as efficient photothermal reagent and H2S responsive acceptor. Significantly, the photothermal signal of CPB could be obviously reduced after challenged with H2S ascribed to synchronous reaction between the ferric ion (Fe3+) and H2S. The improved walking area and freedom enable significant signal amplification, enhancing the biosensor's performance. Under ideal circumstances, the proposed photothermal assay demonstrated excellent performance for determination of miRNA-21.

Self-passivated CuV2O6 as a universal photoelectrode material for reliable and accurate photoelectrochemical sensing

Photoelectrochemical (PEC) detection has attracted intensive attention during the past decade. Currently, most research focuses on improving the sensitivity and selectivity of the PEC sensor, but the issue of the stability of the photoelectrode material under the testing environment is often ignored or lacks in-depth investigation. Herein, we develop a novel CuV2O6 photoelectrode exhibiting superior stability under the testing environment through self-passivation. CuV2O6-based PEC sensors are fabricated for the first time for highly selective carcinoembryonic antigen (CEA) and human serum alpha fetoprotein (AFP) detection. The CuV2O6 shows great potential as a universal photoelectrode material for reliable and accurate PEC detection of macromolecules.

A new photoelectrochemical biosensor based on FeOOH and exonuclease III-aided dual recycling signal amplification for HPV-16 detection

Herein, based on iron oxyhydroxide (FeOOH) as the photoactive material and exonuclease III (exo III)-aided dual recycling signal amplification, a new photoelectrochemical (PEC) biosensor was successfully developed for human papillomavirus-16 (HPV-16) detection with a wide linear range from 0.5 fM to 1 nM and a low detection limit of 0.17 fM.

A Sensitive Fluorescent Assay for Tetracycline Detection Based on Triple-helix Aptamer Probe and Cyclodextrin Supramolecular Inclusion

Herein, an effective pyrene excimer signaled fluorescent biosensor for the determination of tetracycline based on triple-helix aptamer probe (TAP) and supramolecular inclusion of cyclodextrin was reported. The TAP was devised containing an aptamer loop, two DNA segment stems and a triplex-forming oligonucleotide (signal probe) labeled with pyrenes at 5' and 3' ends. The presence of target could result in its binding towards aptamer with a mighty affinity, leading to a conformation change of the TAP and whereupon the release of the signal probe. This liberty of signal probe enabled the formation of pyrene excimer, generating fluorescence signals. Further, signal amplification was fulfilled through the addition of γ-cyclodextrin which could interact with pyrene dimer, thus leading to an enhanced "on-state" of the sensing ensemble. In contrast, when the target was absent, the sensing ensemble remained "off-state" because of the long distance between two pyrene molecules. When the conditions were properly optimized, the increasing signal kept a linear dependence on target concentrations ranging from 5.0 nM to 100 nM, and the detection limit reached as low as 1.6 nM. In this way, a newly-constructed, simple, and economically affordable protocol enjoys desirable efficiency, sensitivity, specificity in biosensing. Also, its universality as another attractive behalf in assaying diverse targets was envisioned with only the need of matched aptamer replacement.