CuBr2/EDTA-mediated ATRP for ultrasensitive fluorescence detection of lung cancer DNA

A Co-Reactive Immunosensor Based on Ti3C2Tx MXene@TiO2-MoS2 Hybrids Promoting luminol@Au@Ni-Co NCs Electrochemiluminescence for CYFRA 21-1 Detection

The construction of assays is capable of accurately detecting cytokeratin-19 (CYFRA 21-1), which is critical for the rapid diagnosis of nonsmall cell lung cancer. In this work, a novel electrochemiluminescence (ECL) immunosensor based on the co-reaction promotion of luminol@Au@Ni-Co nanocages (NCs) as ECL probe by Ti3C2Tx MXene@TiO2-MoS2 hybrids as co-reaction accelerator was proposed to detect CYFRA 21-1. Ni-Co NCs, as a derivative of Prussian blue analogs, can be loaded with large quantities of Au NPs, luminol, and CYFRA 21-1 secondary antibodies due to their high specific surface area. To further improve the sensitivity of the developed ECL immunosensor, Ti3C2Tx MXene@TiO2-MoS2 hybrids were prepared by in situ growth of TiO2 nanosheets on highly conductive Ti3C2Tx MXene, and MoS2 was homogeneously grown on Ti3C2Tx MXene@TiO2 surfaces by the hydrothermal method. Ti3C2Tx MXene@TiO2-MoS2 hybrids possess excellent catalytic performance on the electro-redox of H2O2 generating more O2·- and obtaining optimal ECL intensity of the luminol/H2O2 system. Under the appropriate experimental conditions, the quantitative detection range of CYFRA 21-1 was from 0.1 pg mL-1 to 100 ng mL-1, and the limit of detection (LOD) was 0.046 pg mL-1. The present sensor has a lower LOD with a wider linear range, which provides a new analytical assay for the early diagnosis of small-cell-type lung cancer labels.

Vitamin B12-catalyzed electro-polymerization for ultrasensitive RNA detection

Vitamin B12 being a natural catalyst in atom transfer radical polymerization (ATRP), has the advantages of mild reaction conditions, good biocompatibility and high catalytic efficiency. In this report, an electrochemical biosensor of the lung cancer biomarker microRNA-21 (miRNA-21) is designed for early screening of lung cancer with high sensitivity at the femtomolar level. In this approach, hairpin DNA with N3 end group was first attached to the electrode surface. When miRNA-21 was present and paired with hairpin DNA, the N3 group released and attached to the ATRP initiator through "click reaction". Through eATRP, a large number of FerrocenylMethyl Methacrylate (FcMMA) monomers polymerized into long chains for signal amplification. These long chains had a distinct electrical signal in the square wave voltammetry (SWV), which can detect RNA with high sensitivity. The limit of detection (LOD) goes down to 1.010 fM after ATRP polymerization, which is lower than that of the majority of other ultra-sensitive RNA electrochemical assays. Results also show that the vitamin B12-based electrochemical biosensor is highly selective and suitable for RNA detection in complex biological samples.

Co-amplification of luminol-based electrochemiluminescence immunosensors based on multiple enzyme catalysis of bimetallic oxides CoCeOx and NiMnO3 for the detection of CYFRA21-1

The accelerated energy supply of co-reactants is an extremely effective strategy for achieving highly sensitive electrochemiluminescence analysis, and binary metal oxides would be an excellent tool for this purpose owing to the nano-enzyme acceleration of mixed metal valence states. Herein, an electrochemiluminescent (ECL) immunosensor for monitoring the concentration of cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) was developed based on a co-amplification strategy triggered by two bimetallic oxides, CoCeO_x and NiMnO₃, with luminol as the luminophore. CoCeO_x derived from an MOF exhibits a large specific surface area and excellent loading capacity as a sensing substrate, and the peroxidase properties enable the catalysis of hydrogen peroxide to provide energy supply to the underlying radicals. The dual enzymatic properties of flower-like NiMnO₃ were employed as probe carriers for luminol enrichment. The peroxidase properties built on Ni²⁺/Ni³⁺ and Mn³⁺/Mn⁴⁺ binary redox pairs resulted in the integration of highly oxidative hydroxyl radicals, and the oxidase properties provided additional superoxide radicals via dissolved oxygen. The practically proven multi-enzyme-catalyzed sandwich-type ECL sensor easily accomplished an accurate immunoassay of CYFRA21-1, harvesting a detection limit of 0.3 pg mL^-1 in the linear range of 0.001-150 ng mL^-1. In conclusion, this work explores the cyclic catalytic amplification of mixed-valence binary metal oxides with nano-enzyme activity in the field of ECL and develops an effective pathway for ECL immunoassay.

A portable and partitioned DNA hydrogel chip for multitarget detection

A DNA hydrogel, owing to its dual properties of liquid and solid, is considered to be an ideal material for constructing biosensors that can integrate the advantages of both wet chemistry and dry chemistry. Nevertheless, it has struggled to cope with the demands of high-throughput analysis. A partitioned and chip-based DNA hydrogel is a potential avenue to achieve this, but currently remains a formidable challenge. Here, we developed a portable and partitioned DNA hydrogel chip that can be used for multitarget detection. The partitioned and surface-immobilized DNA hydrogel chip was formed by inter-crosslinking amplification by incorporating target-recognizing fluorescent aptamer hairpins into multiple rolling circle amplification products, which can achieve portable and simultaneous detection of multiple targets. This approach expands the application of semi-dry chemistry strategies, which can realize high throughput and point of care testing (POCT) of different targets, improving the development of hydrogel-based bioanalysis and providing new potential solutions for biomedical detection.

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.

Nucleotide detection mechanism and comparison based on low-dimensional materials: A review

The recent pandemic has led to the fabrication of new nucleic acid sensors that can detect infinitesimal limits immediately and effectively. Therefore, various techniques have been demonstrated using low-dimensional materials that exhibit ultrahigh detection and accuracy. Numerous detection approaches have been reported, and new methods for impulse sensing are being explored. All ongoing research converges at one unique point, that is, an impetus: the enhanced limit of detection of sensors. There are several reviews on the detection of viruses and other proteins related to disease control point of care; however, to the best of our knowledge, none summarizes the various nucleotide sensors and describes their limits of detection and mechanisms. To understand the far-reaching impact of this discipline, we briefly discussed conventional and nanomaterial-based sensors, and then proposed the feature prospects of these devices. Two types of sensing mechanisms were further divided into their sub-branches: polymerase chain reaction and photospectrometric-based sensors. The nanomaterial-based sensor was further subdivided into optical and electrical sensors. The optical sensors included fluorescence (FL), surface plasmon resonance (SPR), colorimetric, and surface-enhanced Raman scattering (SERS), while electrical sensors included electrochemical luminescence (ECL), microfluidic chip, and field-effect transistor (FET). A synopsis of sensing materials, mechanisms, detection limits, and ranges has been provided. The sensing mechanism and materials used were discussed for each category in terms of length, collectively forming a fusing platform to highlight the ultrahigh detection technique of nucleotide sensors. We discussed potential trends in improving the fabrication of nucleotide nanosensors based on low-dimensional materials. In this area, particular aspects, including sensitivity, detection mechanism, stability, and challenges, were addressed. The optimization of the sensing performance and selection of the best sensor were concluded. Recent trends in the atomic-scale simulation of the development of Deoxyribonucleic acid (DNA) sensors using 2D materials were highlighted. A critical overview of the challenges and opportunities of deoxyribonucleic acid sensors was explored, and progress made in deoxyribonucleic acid detection over the past decade with a family of deoxyribonucleic acid sensors was described. Areas in which further research is needed were included in the future scope.

Antigen-Down PEC Immunosensor for CYFRA21-1 Detection Based on Photocurrent Polarity Switching Strategy

In this work, an antigen-down photoelectrochemical (PEC) immunosensor based on a signal polarity switching strategy for the detection of cytokeratin 19 fragment 21-1 (CYFRA21-1) was proposed. 3,4,9,10-Perylene tetracarboxylic acid (PTCA) is a conjugated organic dye containing five benzene nuclei, which has excellent film-forming and optical properties. PTCA sensitized by SnS₂ can further improve the basal signal and the stability of the PEC immunosensor. Moreover, avidin-functionalized CuInS₂ as a signal probe can convert the basal anodic photocurrent to a cathodic photocurrent. Therefore, the PEC sensor realized the photocurrent polarity conversion before and after labeling. With avidin-functionalized CuInS₂, the polarity of the photocurrent was changed once CYFRA21-1 was detected. Therefore, the PEC immunosensor owns high sensitivity. The linear range of the immunosensor for the detection of CYFRA21-1 is 0.00001-500 ng·mL^-1, and the detection limit is 3.5 fg·mL^-1. The PEC immunosensor has good stability, high selectivity, and good repeatability. This work may provide a new way for the detection of CYFRA21-1 and other proteins.

Electrochemical detection of alkaline phosphatase activity via atom transfer radical polymerization

Alkaline phosphatase (ALP) activity is a diagnostic indicator for a variety of clinical diseases. In this study, an electrochemical method for detecting ALP activity through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) was developed. Specifically, 3-mercaptopropionic (MPA) was firstly fixed on the electrode through sulfur-gold bonding. Subsequently, α-bromophenylacetic acid (BPAA) as initiator was attached to MPA through the recognized carboxylate-Zr4+-phosphate chemistry. Finally, in the existence of ALP, L-Ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS) was hydrolyzed to produce ascorbic acid (AA) which participated in the ARGET ATRP reaction, grafting polymer containing plenty of ferrocene electroactive probes on the surface of electrode. Under optimal experimental conditions, this method had a linear scope of 20-200 mU mL-1, and a limit of detection (LOD) of 1.64 mU mL-1. In addition, the proposed method had good selectivity as well as anti-interference capability, with satisfactory results in inhibition rate and human serum experiments. By merits of good analytical performance, easy operation, and low cost, such a method for ALP activity detection has promising applications in ALP-related disease detection and inhibitor screening.