Near-infrared light-induced homogeneous photoelectrochemical biosensor based on 3D walking nanomotor-assisted CRISPR/Cas12a for ultrasensitive microRNA-155 detection

The dysregulation of microRNA (miRNA) expression levels is intricately linked to a myriad of human diseases, and the precise and delicate detection thereof holds paramount significance in the realm of clinical diagnosis and therapy. Herein, a near-infrared (NIR) light-mediated homogeneous photoelectrochemical (PEC) biosensor was constructed for miRNA-155 detection based on NaYF4: Yb, Tm@ZnIn2S4 (NYF@ ZIS) coupled with a three-dimensional (3D) walking nanomotor-assisted CRISPR/Cas12a strategy. The upconverted light emitted by the NYF in the visible and UV region upon NIR light excitation could be utilized to excite ZIS to produce a photocurrent response. The presence of target miRNA-155 initiated an amplification reaction within the 3D walking nanomotor, resulting in the production of multiple nucleic acid fragments. These fragments could activate the collateral cleavage capability of CRISPR/Cas12a, leading to the indiscriminate cleavage of single-stranded DNA (ssDNA) on ALP-ssDNA-modified magnetic beads and the subsequent liberation of alkaline phosphatase (ALP). The released ALP facilitated the catalysis of ascorbic acid 2-phosphate to generate ascorbic acid as the electron donor to capture the photogenerated holes on the NYF@ZIS surface, resulting in a positively correlated alteration in the photocurrent response. Under optimal conditions, the NIR light-initiated homogeneous PEC biosensor had the merits of good linear range (0.1 fM to 100 pM), an acceptable limit of detection (65.77 aM) for miRNA-155 detection. Considering the pronounced sensitivity, light stability, and low photodamage, this strategy presents a promising platform for detecting various other miRNA biomarkers in molecular diagnostic practice.

A ZnIn2S4/Ag2CO3 Z-scheme heterostructure-based photoelectrochemical biosensor for neuron-specific enolase

An efficient photo-to-electrical signal is pivotal to photoelectrochemical (PEC) biosensors. In our work, a novel PEC biosensor was fabricated for the detection of neuron-specific enolase (NSE) based on a ZnIn2S4/Ag2CO3 Z-scheme heterostructure. Due to the overlapping band potentials of the ZnIn2S4 and Ag2CO3, the formed Z-scheme heterostructure can promote the charge separation and photoelectric conversion efficiency. And the concomitant Ag nanoparticles in Ag2CO3 provided multiple functions to enhance the PEC response of the Z-scheme heterostructure. It acts not only as a bridge for the transfer of carriers between ZnIn2S4 and Ag2CO3, promoting the constructed Z-scheme heterostructure, but also as electron mediators to accelerate the transfer of photogenerated carriers and improve the capture of visible light of the Z-scheme heterostructure by surface plasmon resonance (SPR). Compared with single Ag2CO3 and ZnIn2S4, the photocurrent of the designed Z-scheme heterostructure increased more than 20 and 60 times respectively. The fabricated PEC biosensor based on a ZnIn2S4/Ag2CO3 Z-scheme heterostructure exhibits sensitive detection to NSE, and presents a linear range of 50 fg·mL-1 ~ 200 ng·mL-1 with a limit of detection of 4.86 fg·mL-1. The proposed PEC biosensor provides a potential approach for clinical diagnosis.

Highly efficient photocathodic cascade material for constructing sensitive photoelectrochemical biosensor

Photocathodic biosensor possesses excellent anti-interference capability in bioanalysis, which however suffers from high electron-hole recombination rate with low photocurrent. Herein, a high-performance inorganic organic P₃HT@C₆₀@ZnO nanosphere with cascade energy band arrangement was synthesized as photoactive signal probe, which inherited the advantages of inorganic strong optical absorptivity and organic high mobility for photo-generated holes. Specifically, the well-matched band gap endowed not only the improved life for light generated carrier and promoted separation of electron-hole pairs, but also the expansion of charge-depletion layer, significantly improving the photoelectric conversion efficiency for acquiring an extremely high photocathodic signal that increased by 30 times compared with individual materials. Accordingly, by integrating with the efficient amplification of DNA nanonet derived from clamped hybrid chain reaction (C-HCR), a sensitive P₃HT@C₆₀@ZnO nanosphere based photocathodic biosensor was proposed for accurate detection of p53. The experimental results showed that the biosensor had a wide detection range from 0.1 fM to 10 nM and a low detection limit of 0.37 fM toward p53, offering a new avenue to construct sensitive PEC platform with superior anti-interference ability and hold a prospective application in early disease diagnosis and biological analysis.

A Branched Rutile/Anatase Phase Structure Electrode with Enhanced Electron-Hole Separation for High-Performance Photoelectrochemical DNA Biosensor

A photoelectrochemical (PEC) detection platform was built based on the branched rutile/anatase titanium dioxide (RA-TiO₂) electrode. Theoretical calculations proved that the type-II band alignment of rutile and anatase could facilitate charge separation in the electrode. The self-generated electric field at the interface of two phases can enhance the electron transfer efficiency of the electrode. Carboxylated CdTe quantum dots (QDs) were applied as signal amplification factors. Without the target DNA presence, the CdTe QDs were riveted to the surface of the electrode by the hairpin probe DNA. The sensitization of CdTe QDs increased the photocurrent of the electrode significantly. When the target DNA was present, the structural changes of the hairpin probe DNA resulted in the failure of the sensitized structure. Benefiting from excellent electrode structure design and CdTe QDs sensitization strategy, the PEC assays could achieve highly sensitive and specific detection of target DNA in the range of 1 fM to 1 nM, with a detection limit of 0.23 fM. The electrode construction method proposed in this article can open a new avenue for the preparation of more efficient PEC sensing devices.

Dual-sensitized heterojunction PDA/ZnO@MoS2 QDs combined with multilocus domino-like DNA cascade reaction for ultrasensitive photoelectrochemical biosensor

In this work, by integrating with a highly efficient multilocus domino-like cascade reaction on DNA nanonet, an ultrasensitive PEC biosensor based on dual-sensitized PDA/ZnO@MoS₂ QDs photoactive material as signal probe was proposed for detection of miRNA-182-5p. The dual-sensitized PDA/ZnO@MoS₂ QD composed by both of p-n and S-scheme heterojunctions on electrode generated an extremely high initial PEC signal, which however quenched by CdTe QDs decorated on DNA nanonet owing to the significant p-n quenching effect. Thereafter, the output DNA (RS) from DSN enzyme-assisted target recycling amplification triggered an ingenious multilocus domino-like DNA cascade reaction on DNA nanonet for releasing numerous CdTe QDs. Thanks to the multilocus domino-like mode that owned abundant binding sites for increasing trigger efficiency and drove cascade reaction automatically advance along four stated pathways, the target conversion rate could be improved effectively compared with that of traditional approaches, significantly enhancing the detection sensitivity. Consequently, the developed PEC biosensor exhibited a low detection limit to 0.17 fM, providing a new avenue for sensitive, fast and reliable sensing of various DNA/RNA.

A Label-Free Photoelectrochemical Biosensor Based on CRISPR/Cas12a System Responsive Deoxyribonucleic Acid Hydrogel and "Click" Chemistry

A novel label-free photoelectrochemical (PEC) biosensor is presented in this work. As a barrier, the DNA hydrogel could block the coupling between g-C₃N₄ and CdS quantum dots (QDs). Therefore, extremely low photocurrent signals were obtained. The presence of target microRNA-21 can initiate the rolling circle amplification (RCA) reaction, which in turn produces many repeated sequences to activate the CRISPR/Cas12a system. The trans-cleavage activity of the CRISPR/Cas12a system led to the degradation of DNA hydrogels efficiently. As a result, the g-C₃N₄/CdS QDs heterojunction was formed through "click" chemistry. Through the amplification of the RCA and CRISPR/Cas12a system, the sensitivity of the PEC biosensor was improved significantly with the detection limit of 3.2 aM. The proposed sensor also showed excellent selectivity and could be used to detect actual samples. In addition, the modular design could facilitate the detection of different objects. Thus, the proposed CRISPR/Cas12a system responsive DNA hydrogel provides a simple, sensitive, and flexible way for label-free PEC analysis.

Boosting the Photocatalytic Ability of TiO2 Nanosheet Arrays for MicroRNA-155 Photoelectrochemical Biosensing by Titanium Carbide MXene Quantum Dots

The electrodes of two-dimensional (2D) titanium dioxide (TiO₂) nanosheet arrays were successfully fabricated for microRNA-155 detection. The (001) highly active crystal face was exposed to catalyze signaling molecules ascorbic acid (AA). Zero-dimensional (0D) titanium carbide quantum dots (Ti₃C₂T_x QDs) were modified to the electrode as co-catalysts and reduced the recombination rate of the charge carriers. Spectroscopic methods were used to determine the band structure of TiO₂ and Ti₃C₂T_x QDs, showing that a type Ⅱ heterojunction was built between TiO₂ and Ti₃C₂T_x QDs. Benefiting the advantages of materials, the sensing platform achieved excellent detection performance with a wide liner range, from 0.1 pM to 10 nM, and a low limit of detection of 25 fM (S/N = 3).

Enzyme-free nucleic acid dual-amplification strategy combined with mimic enzyme catalytic precipitation reaction for the photoelectrochemical detection of microRNA-21

A novel photoelectrochemical (PEC) biosensor based on an enzyme-free nucleic acid dual-amplification strategy combined with a mimic enzyme to catalyze the deposition of a quencher is reported for the ultrasensitive detection of miRNA-21. A limited amount of target miRNA-21 can trigger the formation of long DNA duplexes on the electrode, owing to the synergistic effect of the enzyme-free nucleic acid dual-amplification strategy of entropy-driven strand displacement reaction (ESDR) amplification and hybridization chain reaction (HCR) amplification. The embedded manganese porphyrin (MnPP) in the long DNA duplexes acts as a horseradish peroxidase (HRP)-mimicking enzyme to catalyze the transformation of benzo-4-chlorohexadienone on the electrode surface, resulting in a significant reduction in photocurrent intensity. As a photosensitive material, BiOCl-BiOI is used as a tag to provide strong initial PEC signals. Based on the cascade integration of the enzyme-free nucleic acid dual-amplification strategy and the mimic enzyme-catalyzed precipitation reaction, the current PEC biosensor exhibits outstanding performance for miRNA-21 detection with an ultralow detection limit (33 aM) and a wide quantification range (from 100 aM to 1 nM). This work provides a new avenue toward the ultrasensitive detection of miRNAs, and is expected to be used for clinical and biochemical samples. A unique PEC biosensor with the BiOCl-BiOI composite, as the photosensitive material, has been developed for ultrasensitive miRNA-21 determination based on the combination of an enzyme-free nucleic acid dual-amplification strategy and mimic enzyme catalytic precipitation reaction.

In-situ engineered MXene-TiO2/ BiVO4 hybrid as an efficient photoelectrochemical platform for sensitive detection of soluble CD44 proteins

Interfacial charge-carrier recombination is a bottle-neck issue restricting photoelectrochemical biosensors advancement in the wearable clinical electronics. In this study, we propose a simple approach to construct a highly efficient photoactive heterojunction capable of functioning as an active substrate in PEC biosensing of CD44 proteins. Taking the advantage of high photocatalytic activity of BiVO₄, and biocompatible yet conductive 2D-Ti₃C₂T_x nanosheets, a workable heterojunction was constructed between in-situ formed TiO₂ from the partially oxidized Ti₃C₂T_x and lysine functionalized BiVO₄ (TiO₂/MX-BiVO₄). The interfacial arrangement was ideal for promoting fast charge transfer from photo-excited BiVO₄ and TiO₂ to Ti₃C₂T_x, constructing an energy level-cascade that permits minimal charge-carrier recombination besides robust photocatalytic redox activity. The PEC biosensor relies on the ligand-protein interaction, where hyaluronic acid was directly immobilized over TiO₂/MX-BiVO₄ based on the interactions between carboxyl of lysine and amino moieties of hyaluronic acid. The PEC biosensor response depends on the inhibition in the measured photo-oxidation current of mediator species, i.e., ascorbic acid after the addition of CD44 proteins. The superior photo-activity, and robust heterojunction arrangement, produced a sensitive signal capable of recognizing CD44 in the wide concentration window of 2.2 × 10^-4 ng mL^-1 to 3.2 ng mL^-1 with a low-detection limit of 1.4 × 10^-2 pg mL^-1. The strong interaction between lysine functionalized BiVO₄ and hyaluronic acid enabled biosensor to exhibit robust antifouling characteristics towards similar proteins such as PSA and NSE. The quantification of CD44 protein from real-blood serum samples further confirmed the biosensor's reliability for clinical application.