A sensitive label-free photoelectrochemical aptasensor based on a novel PTB7-Th/H2O2 system with unexpected photoelectric performance for C-reactive protein analysis

Electrochemical biosensor based on RNA aptamer and ferrocenecarboxylic acid signal probe for C-reactive protein detection

Monitoring health-related biomarkers using fast and facile detection techniques provides key physicochemical information for disease diagnosis or reflects body health status. Among them, electrochemical detection of various bio-macromolecules, e.g., the C-reactive protein (CRP), is of great interest in offering potential diagnosis for acute inflammation caused by infections, heart diseases, etc. Herein, a novel electrochemical aptamer biosensor was constructed from Ti3C2Tx MXene and in-situ reduced Au NPs for thiolated-RNA aptamer immobilization and CRP protein detection using Fc(COOH) as the signal probe. The sensory performances for CRP detection were optimized based on working conditions, including the incubation times and the pH. The large surface area offered by Ti3C2Tx MXene and high electrical conductivity originating from Au NPs endowed the as-fabricated aptamer biosensor with a decent sensitivity for CRP in a wide linear range of 0.05-80.0 ng/mL, good selectivity over interfering substances, and a low detection limit of 0.026 ng/mL. Such aptamer biosensors also detected CRP in serum samples using the spike & recovery method with reasonable recovery rates. The results demonstrated the potential of the as-fabricated electrochemical aptamer biosensor for fast and facile CRP detection in practical applications.

Dual-mode colorimetric and homogeneous electrochemical detection of intracellular/extracellular H2O2 based on FeSx/SiO2 nanoparticles with high peroxidase-like activity

Abnormal expression of hydrogen peroxide (H₂O₂) elucidates cell dysfunctions and might induce the occurrence and deterioration of various diseases. However, limited by its ultralow level under pathophysiological conditions, intracellular and extracellular H₂O₂ was difficult to be detected accurately. Herein, a colorimetric and homogeneous electrochemical dual-mode biosensing platform was constructed for intracellular/extracellular H₂O₂ detection based on FeS_x/SiO₂ nanoparticles (FeS_x/SiO₂ NPs) with high peroxidase-like activity. In this design, FeS_x/SiO₂ NPs were synthesized with excellent catalytic activity and stability compared to natural enzymes, which improved the sensitivity and stability of sensing strategy. 3,3',5,5'-Tetramethylbenzidine (TMB), as a multifunctional indicator, was oxidized in the presence of H₂O₂, generated color changes and realized visual analysis. In this process, the characteristic peak current of TMB decreased, which could realize the ultrasensitive detection of H₂O₂ by homogeneous electrochemistry. Accordingly, by integrating visual analysis ability of colorimetry and the high sensitivity of homogeneous electrochemistry, the dual-mode biosensing platform exhibited high accuracy, sensitivity and reliability. The detection limits of H₂O₂ were 0.2 μM (S/N = 3) for the colorimetric method and 2.5 nM (S/N = 3) for the homogeneous electrochemistry assay. Therefore, the dual-mode biosensing platform provided a new opportunity for highly accurate and sensitive detection of intracellular/extracellular H₂O₂.

Au nano-flower/organic polymer heterojunction-based cathode photochemical biosensor with reduction-accelerated quenching effect of porphyrin manganese

In this work, a novel reduction-accelerated quenching of manganese porphyrin (MnPP) based signal-off cathode photochemical (PEC) biosensor by using Au nano-flower/organic polymer (PTB7-Th) heterojunction as platform was proposed for ultrasensitive detection of Hg²⁺. Firstly, the photoactive PTB7-Th with Au nano-flower on electrode could form a typical Mott-Schottky heterojunction for acquiring an extremely high cathode signal. Meanwhile, the presence of target Hg²⁺ could bring in the formation of T-Hg²⁺-T based scissor-like DNA walker, which thus activated efficient Mg²⁺-specific DNAzyme based cleavage recycling to shear hairpin H2 on electrode to exposure abundant trigger sites of hybridization chain reaction (HCR) for in-situ decoration of quencher MnPP. Here, besides the steric hinderance and light competition effect of MnPP decorated DNA nanowires attributing to signal decrease, we for the first time testified the MnPP reduction-accelerated quenching that constantly consumed the photo-generated electron by using cyclic voltammetry (CV). As a result, the proposed biosensor had excellent sensitivity and selectivity to Hg²⁺ in the range of 1 fM-10 nM with a detection limit of 0.48 fM. The actual sample analysis showed that the biosensor could reliably and quantitatively identify Hg²⁺, indicating an excellent application prospect in routine detection.

Self-Supplied Electron Photoelectrochemical Biosensor with PTB7-Th as a Photoelectric Material and Biotin as an Efficient Quencher

In this work, a self-supplied electron photoelectrochemical (PEC) biosensor for sensitive determination of Pb²⁺ was established by utilizing donor-acceptor (D-A)-type PTB7-Th (poly{4,8-bis[5-(2-ethylhexyl) thiophen-2-yl]benzo[1,2-b,4,5-b']dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]-thiophene-4,6-diyl}) as a photoelectric material coupled with biotin as an efficient signal quencher. Impressively, compared with the traditional PEC signal quenchers, biotin was first applied as a PEC signal quencher in this work and it effectively avoided a cumbersome preparation process, complex DNA sequence design, and extra reagent assistance and greatly simplified experimental steps, which could achieve an efficient PEC signal quenching toward PTB7-Th. In addition, the execution of a DNAzyme-assisted Pb²⁺ recycling amplification reaction could release the quencher biotin, leading to the recovery of the PEC signal, thereby realizing the quantitative detection of Pb²⁺. Resultantly, the submitted self-supplied electron PEC biosensor presented an extensive coverage of assay Pb²⁺ (50 fM to 500 nM) along with a low determination limit (16.7 fM), which exhibited the advantages of high selectivity and excellent stability. Importantly, this work provided a powerful alternative to traditional heavy metal-ion assessment methods and possessed the potential for application in environment, biomedicine, and food-safety fields.

Transition orbital projection approach for excited state tracking

Quantitively comparing the features between different electronic excited states (ESs) is a crucial task in both potential energy surface (PES) studies and excited-state fragmentation approaches. However, it is still a challenging problem in regard to the comparison of complex and highly degenerate systems. Herein, we present a transition orbital projection (TOP) method to calculate the similarity of different ESs based on the configuration vectors of two types of transition densities. It fully considers four significant problems, including phase, hole-particle bijectivity, orbital permutation, and sign of configuration coefficients. TOP state-tracking-based excited-state optimization shows high robustness in several high-symmetric systems, which are difficult to describe with traditional state-tracking approaches. The TOP state-tracking method is expected to be widely applied to the PES of photochemical reactions, ES molecular dynamics to track the diabatic states, and fragmentation approaches for local excitation of large systems.

Single-Molecule Identification of the Conformations of Human C-Reactive Protein and Its Aptamer Complex with Solid-State Nanopores

Human C-reactive protein (CRP) is an established inflammatory biomarker and was proved to be potentially relevant to disease pathology and cancer progression. A large body of methodologies have been reported for CRP analysis, including electrochemical/optical biosensors, aptamer, or antibody-based detection. Although the detection limit is rather low until pg/uL, most of which are time-consuming and relatively expensive, and few of them provided CRP single-molecule information. This work demonstrated the nanopore-based approach for the characterization of CRP conformation under versatile conditions. With an optimized pore of 14 nm in diameter, we achieved the detection limit as low as 0.3 ng/μL, voltage polarity significantly influences the electro-osmotic force and CRP translocation behavior, and the pentameric conformation of CRP may dissociate into pro-inflammatory CRP isoforms and monomeric CRP at bias potential above 300 mV. CRP tends to translocate through nanopores faster along with the increase in pH values, due to more surface charge on both CRP and pore inner wall and stronger electro-osmotic force. The CRP could specifically bind with its aptamer of different concentrations to form complexes, and the complexes exhibited distinguishable nanopore translocation behavior compared with CRP alone. The variation of the molar ratio of aptamer significantly influences the orientation of CRP translocation. The plasma test under physiological conditions displayed the ability of the nanopore system on the CRP identification with a concentration of 3 ng/μL.

Electroanalytical point-of-care detection of gold standard and emerging cardiac biomarkers for stratification and monitoring in intensive care medicine - a review

Determination of specific cardiac biomarkers (CBs) during the diagnosis and management of adverse cardiovascular events such as acute myocardial infarction (AMI) has become commonplace in emergency department (ED), cardiology and many other ward settings. Cardiac troponins (cTnT and cTnI) and natriuretic peptides (BNP and NT-pro-BNP) are the preferred biomarkers in clinical practice for the diagnostic workup of AMI, acute coronary syndrome (ACS) and other types of myocardial ischaemia and heart failure (HF), while the roles and possible clinical applications of several other potential biomarkers continue to be evaluated and are the subject of several comprehensive reviews. The requirement for rapid, repeated testing of a small number of CBs in ED and cardiology patients has led to the development of point-of-care (PoC) technology to circumvent the need for remote and lengthy testing procedures in the hospital pathology laboratories. Electroanalytical sensing platforms have the potential to meet these requirements. This review aims firstly to reflect on the potential benefits of rapid CB testing in critically ill patients, a very distinct cohort of patients with deranged baseline levels of CBs. We summarise their source and clinical relevance and are the first to report the required analytical ranges for such technology to be of value in this patient cohort. Secondly, we review the current electrochemical approaches, including its sub-variants such as photoelectrochemical and electrochemiluminescence, for the determination  of important CBs highlighting the various strategies used, namely the use of micro- and nanomaterials, to maximise the sensitivities and selectivities of such approaches. Finally, we consider the challenges that must be overcome to allow for the commercialisation of this technology and transition into intensive care medicine.

A highly sensitive photoelectrochemical aptasensor based on BiVO4 nanoparticles-TiO2 nanotubes for detection of PCB72

In this work, a simple and highly sensitive photoelectrochemical (PEC) aptasensor has been developed for detecting PCB72 based on TiO₂ nanotubes (NTs) decorated with BiVO₄ nanoparticles (NPs). The BiVO₄ NPs-TiO₂ NTs composites prepared through a simple hydrothermal method exhibit good visible-light adsorption ability, high PEC response and perfect photo-excited stability. The synthesized composites were explored as the photoactive sensing materials for development of a PEC sensing platform for the first time. Here, Au nanoparticles (NPs) were first deposited the composites, and the anti-PCB72 aptamer molecules were immobilized on the Au NPs-deposited BiVO₄ NPs-TiO₂ NTs. The developed PEC aptasensor exhibits high sensitivity and specificity for PCB72 with a wide linear range from 1 ng/L to 500 ng/L and a low detection limit of 0.23 ng/L. The application of the aptasensor was evaluated by determining PCB 72 in the environment water samples. Thus, a simple and efficient PEC sensing platform was established for detecting the content of PCBs in the environment.