Bioinspired Electro-RAFT Polymerization for Electrochemical Sensing of Nucleic Acids

Enzyme-free fluorescent DNA detection based on nucleic acid-templated click reaction via controllable synthesis of Cu2O as heterogeneous nanocatalyst

In the field of nucleic acid amplification assays, developing enzyme-free, easy-to-use, and highly sensitive amplification approaches remains a challenge. In this work, we synthesized a heterogeneous Cu2O nanocatalyst (hnCu2O) with different particle sizes and shapes, which was used for developing enzyme- and label-free nucleic acid amplification methods based on the nucleic acid-templated azide-alkyne cycloaddition (AAC) reaction catalyzed by hnCu2O. The hnCu2O exhibited size- and shape-dependent catalytic activity, with smaller sizes and spherical-like shapes exhibiting superior activity. Spherical-like hnCu2O (61 ± 8 nm) not only achieved a ligation yield of up to 84.2 ± 3.9 % in 3 min but also exhibited faster kinetics in the nucleic acid-templated hnCu2O-catalyzed AAC reaction, with a high reaction rate of 0.65 min-1 and a half-life of 1.07 ± 0.09 min. Based on this result, we developed nucleic acid-templated click ligation linear amplification reaction (NA-CLLAR) and nucleic acid-templated click ligation exponential amplification reaction (NA-CLEAR) approach. By combining the recognition (complementary to the target sequence) and signal output (split G-quadruplex sequence) elements into a DNA probe, the NA-CLLAR and NA-CLEAR fluorescence assays achieved highly specific detection of target nucleic acids, with a detection limit of 2.8 aM based on G-quadruplex-enhanced fluorescence. This work is a valuable reference and will inspire researchers to design enzyme-free nucleic acid signal amplification strategies by developing different types of Cu(I) catalysts with improved catalytic activity.

A facile electrochemical immunosensor based on EDTA-Pb2+ complexation reaction

The sensitivity of electrochemical (EC) sensors has been improved through the development of multiple approaches. However, the majority of EC sensors were limited in their practical application by high costs or tedious procedures. Herein, based on ethylenediaminetetraacetic acid (EDTA)-Pb2+ complexation reaction, a facile and affordable immunosensor was designed. Pb2+-magnesium silicate hydrate was served as the sensing substrate. The immunorecognition process was carried out in the Eppendorf tube, and antibody-functionalized Pb2+-polydopamine was utilized as immunoprobe. In the tube, the quantitative and appropriate excess of EDTA was introduced to complex with Pb2+ on the immunoprobes. The remaining EDTA was added to the sensing substrate surface to coordinate with some Pb2+ in it. This leaded to the reduction of the EC signal of Pb2+, which was related to the antigen concentration. Using prostate-specific antigen as the model analyte, the sensitive detection was realized with a low limit of detection (30.49 fg mL-1). Remarkably, the assay results were available within 24 min, sensibly faster than the most existing EC sensors.

CRISPR-empowered electrochemical biosensor for target amplification-free and sensitive detection of miRNA

The clustered regularly interspaced short palindromic repeats (CRISPR) system provides a new molecular diagnostic tool for construction of biosensor platforms due to its high programmability and target specificity. Herein, we developed a CRISPR-empowered electrochemical biosensor by combining the advantages of CRISPR/Cas13a and primer exchange reaction (PER), named PER-E-CRISPR, for target amplification-free and sensitive detection of miR-21. Dual-signal amplification procedures involve the binding of target miR-21 induced by CRISPR-based amplification, along with the hybridization of multiple short single-stranded DNA strands with PER concatemers. When target miR-21 is present, CRISPR/Cas13a specifically recognizes the target miRNA, triggering the trans-cleavage activity of CRISPR/Cas13a. Then Cas13a/crRNA/miRNA cleaved the predesigned ribonucleotide site in hairpin 1 (HP1) and released trigger to open hairpin 2 (HP2) modified on the electrode surface. Then PER bridge sequence contained in HP2 is exposed and hybridized with PER concatemers, following multiple short single-stranded DNA tagged with methylene blue (ssDNA-MB) bond with the PER concatemers. Under optimized conditions, PER-E-CRISPR assay for detecting miR-21 exhibits linearity in dynamic range from 10-13 to 10-7 M, and we obtained a limit of detection (LOD) of 30.2 fM. The established PER-E-CRISPR biosensor shows perfect practical performance in actual plasma, which may have great promising prospects for miRNA detection in the field of molecular diagnosis.

On-site airborne pathogen detection for infection risk mitigation

Human-infecting pathogens that transmit through the air pose a significant threat to public health. As a prominent instance, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that caused the COVID-19 pandemic has affected the world in an unprecedented manner over the past few years. Despite the dissipating pandemic gloom, the lessons we have learned in dealing with pathogen-laden aerosols should be thoroughly reviewed because the airborne transmission risk may have been grossly underestimated. From a bioanalytical chemistry perspective, on-site airborne pathogen detection can be an effective non-pharmaceutic intervention (NPI) strategy, with on-site airborne pathogen detection and early-stage infection risk evaluation reducing the spread of disease and enabling life-saving decisions to be made. In light of this, we summarize the recent advances in highly efficient pathogen-laden aerosol sampling approaches, bioanalytical sensing technologies, and the prospects for airborne pathogen exposure measurement and evidence-based transmission interventions. We also discuss open challenges facing general bioaerosols detection, such as handling complex aerosol samples, improving sensitivity for airborne pathogen quantification, and establishing a risk assessment system with high spatiotemporal resolution for mitigating airborne transmission risks. This review provides a multidisciplinary outlook for future opportunities to improve the on-site airborne pathogen detection techniques, thereby enhancing the preparedness for more on-site bioaerosols measurement scenarios, such as monitoring high-risk pathogens on airplanes, weaponized pathogen aerosols, influenza variants at the workplace, and pollutant correlated with sick building syndromes.

Poly(glycerol monomethacrylate)-encapsulated upconverting nanoparticles prepared by miniemulsion polymerization: morphology, chemical stability, antifouling properties and toxicity evaluation

In this report, upconverting NaYF4:Yb3+,Er3+ nanoparticles (UCNPs) were synthesized by high-temperature coprecipitation of lanthanide chlorides and encapsulated in poly(glycerol monomethacrylate) (PGMMA). The UCNP surface was first treated with hydrophobic penta(propylene glycol) methacrylate phosphate (SIPO) to improve colloidal stability and enable encapsulation by reversible addition-fragmentation chain transfer miniemulsion polymerization (RAFT) of glycidyl methacrylate (GMA) in water, followed by its hydrolysis. The resulting UCNP-containing PGMMA particles (UCNP@PGMMA), hundreds of nanometers in diameter, were thoroughly characterized by transmission (TEM) and scanning electron microscopy (SEM), dynamic light scattering (DLS), infrared (FTIR) and fluorescence emission spectroscopy, and thermogravimetric analysis (TGA) in terms of particle morphology, size, polydispersity, luminescence, and composition. The morphology, typically raspberry-like, depended on the GMA/UCNP weight ratio. Coating of the UCNPs with hydrophilic PGMMA provided the UCNPs with antifouling properties while enhancing chemical stability and reducing the cytotoxicity of neat UCNPs to a non-toxic level. In addition, it will allow the binding of molecules such as photosensitizers, thus expanding the possibilities for use in various biomedical applications.

Electrochemical Biosensors for Whole Blood Analysis: Recent Progress, Challenges, and Future Perspectives

Whole blood, as one of the most significant biological fluids, provides critical information for health management and disease monitoring. Over the past 10 years, advances in nanotechnology, microfluidics, and biomarker research have spurred the development of powerful miniaturized diagnostic systems for whole blood testing toward the goal of disease monitoring and treatment. Among the techniques employed for whole-blood diagnostics, electrochemical biosensors, as known to be rapid, sensitive, capable of miniaturization, reagentless and washing free, become a class of emerging technology to achieve the target detection specifically and directly in complex media, e.g., whole blood or even in the living body. Here we are aiming to provide a comprehensive review to summarize advances over the past decade in the development of electrochemical sensors for whole blood analysis. Further, we address the remaining challenges and opportunities to integrate electrochemical sensing platforms.

An electrochemical PNA-based sensor for the detection of the SARS-CoV-2 RdRP by using surface-initiated-reversible-addition−fragmentation-chain-transfer polymerization technique

Coronavirus disease 2019 is one of the global health problems. Herein, a highly sensitive electrochemical biosensor has been designed to detect the RNA-dependent RNA polymerase (RdRP) of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) (SARS-CoV-2 RdRP). Herein, the surface-initiated reversible-addition-fragmentation-chain-transfer polymerization was used to amplify the electrochemical signal. To do that, the thiol-terminated peptide nucleic acid (PNA) probes were first immobilized on the surface of a screen-printed electrode modified with reduced graphene oxide-gold nanocomposite and then the fixed concentration of the SARS-CoV-2 RdRP was added to the electrode surface to interact with PNA probes. Subsequently, the Zr ⁴⁺ ions were added to interact with the phosphate groups of the SARS-CoV-2 RdRP. It allowed us to polymerase the ferrocenylmethyl methacrylate (FcMMA) and 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid on the SARS-CoV-2 RdRP chain. Since the poly-FcMMA has an electrochemical signal, the response of the PNA-based sensor to SARS-CoV-2 RdRP was increased in the range of 5-500 aM. The limit of detection was calculated to be 0.8 aM which is lower than the previous sensor for SARS-CoV-2 RdRP detection. The proposed PNA-based sensor showed high selectivity to the SARS-CoV-2 RdRP in the presence of the gene fragments of influenza A and Middle East respiratory syndrome coronavirus.

Recent advancements in nucleic acid detection with microfluidic chip for molecular diagnostics

The coronavirus disease 2019 (COVID-19) has extensively promoted the application of nucleic acid testing technology in the field of clinical testing. The most widely used polymerase chain reaction (PCR)-based nucleic acid testing technology has problems such as complex operation, high requirements of personnel and laboratories, and contamination. The highly miniaturized microfluidic chip provides an essential tool for integrating the complex nucleic acid detection process. Various microfluidic chips have been developed for the rapid detection of nucleic acid, such as amplification-free microfluidics in combination with clustered regularly interspaced short palindromic repeats (CRISPR). In this review, we first summarized the routine process of nucleic acid testing, including sample processing and nucleic acid detection. Then the typical microfluidic chip technologies and new research advances are summarized. We also discuss the main problems of nucleic acid detection and the future developing trend of the microfluidic chip.

Hybrid PET Track-Etched Membranes Grafted by Well-Defined Poly(2-(dimethylamino)ethyl methacrylate) Brushes and Loaded with Silver Nanoparticles for the Removal of As(III)

Nanoporous track-etched membranes (TeM) are promising materials as adsorbents to remove toxic pollutants, but control over the pore diameter and density in addition to precise functionalization of nanochannels is crucial for controlling the surface area and efficiency of TeMs. This study reported the synthesis of functionalized PET TeMs as high-capacity sorbents for the removal of trivalent arsenic, As(III), which is more mobile and about 60 times more toxic than As(V). Nanochannels of PET-TeMs were functionalized by UV-initiated reversible addition fragmentation chain transfer (RAFT)-mediated grafting of 2-(dimethyamino)ethyl methacrylate (DMAEMA), allowing precise control of the degree of grafting and graft lengths within the nanochannels. Ag NPs were then loaded onto PDMAEMA-g-PET to provide a hybrid sorbent for As(III) removal. The As(III) removal efficiency of Ag@PDMAEMA-g-PET, PDMAEMA-g-PET, and pristine PET TeM was compared by adsorption kinetics studies at various pH and sorption times. The adsorption of As(III) by Ag@DMAEMA-g-PET and DMAEMA-g-PET TeMs was found to follow the Freundlich mechanism and a pseudo-second-order kinetic model. After 10 h, As(III) removal efficiencies were 85.6% and 56% for Ag@PDMAEMA-g-PET and PDMAEMA-g-PET, respectively, while PET template had a very low arsenic sorption capacity of 17.5% at optimal pH of 4.0, indicating that both PDMAEMA grafting and Ag-NPs loading significantly increased the As(III) removal capacity of PET-TeMs.

Photoswitchable CRISPR/Cas12a-Amplified and Co3O4@Au Nanoemitter Based Triple-Amplified Diagnostic Electrochemiluminescence Biosensor for Detection of miRNA-141

In this work, a CRISPR/Cas12a initiated switchable ternary electrochemiluminescence (ECL) biosensor combined with a Co3O4@Au nanoemitter is presented for the in vitro monitoring of miRNA-141. Benefiting from the advantages of high-throughput cargo payload capability and superconductivity, three-dimensional reduced graphene oxide (3D-rGO) was designated as an introductory conducting stratum of a paper working electrode (PWE). With the collaborative participation of Co3O4@Au NPs, the transmutation of TPrA in the Ru(bpy)32+/TPrA system can be riotously expedited into exorbitant free radical ions TPrA•, which provoked the exaggeration of the ECL signal. Moreover, the programmable enzyme-free hybrid chain reaction (HCR) amplifier on the PWE surface accurately anchored the assembly of nucleic acid tandem and accomplished the secondary recursion of the signal. Impressively, the multifunctional CRISPR/Cas12a with nonspecific cis/trans-splitting decomposition manipulated the photoswitch of the "on-off" signal state that avoided the false-positive diagnosis. The presented multistrategy cooperative biosensor demonstrated extraordinary sensitivity and specificity, with a low detection limit of 3.3 fM (S/N = 3) in the concentration scope from 10 fM to 100 nM, which fully corresponded to the expectation. Overall, this innovative methodology paved a generous avenue for evaluating multifarious biotransformations and provided a tremendous impetus to the development of real-time diagnosis and clinical detection of other biomarkers.