Fluorescence Sensing of Eclampsia Biomarkers via the Immunosorbent Atom Transfer Radical Polymerization Assay.

Accurate and quantitative detection of pre-eclampsia markers is crucial in reducing pregnancy mortality rates. This study introduces a novel approach utilizing a fluorescent biosensor by the immunosorbent atom transfer radical polymerization (immuno-ATRP) assay to detect the pre-eclampsia protein marker CD81. The critical step used in this sensor is the novel signal amplification strategy of fluorescein polymerization mediated by ferritin-enhanced controlled radical polymerization, which combines with a traditional enzyme-linked immunosorbent assay (ELISA) to further reduce the detection limit of the CD81 protein concentration. The fluorescence intensity was linear versus logarithmic CD81 protein concentration from 0.1 to 10,000 pg mL-1, and the detection limit was 0.067 pg mL-1. Surprisingly, in 30% normal human serum (NHS), the sensor can also detect target protein over 0.1-10,000 pg mL-1, with 0.083 pg mL-1 for the detection limit. Moreover, the proposed biosensor is designed to be cost-effective, making it accessible, particularly in resource-limited settings where expensive detection techniques may not be available. The affordability of this method enables widespread screening and monitoring of preeclampsia, ultimately benefiting many pregnant women by improving their healthcare outcomes. In short, developing of a low-cost and susceptible direct detection method for preeclampsia protein markers, such as CD81, through the use of the immuno-ATRP assay, has significant implications for reducing pregnancy mortality. This method holds promise for early detection, precise treatment, and improved management of preeclampsia, thereby contributing to better maternal and fetal health.

Application potential of senolytics in clinical treatment.

Of the factors studied in individual ageing, the accumulation of senescent cells has been considered as an essential cause of organ degeneration to eventually initiate age-related diseases. Cellular senescence is attributed to the accumulation of damage for an inducement in the activation of cell cycle inhibitory pathways, resulting the cell permanently withdraw from the cell proliferation cycle. Further, senescent cells will activate the inflammatory factor secretion pathway to promote the development of various age-related diseases. Senolytics, a small molecule compound, can delay disease development and extend mammalian lifespan. The evidence from multiple trials shows that the targeted killing of senescent cells has a significant clinical application for the treatment of age-related diseases. In addition, senolytics are also significant for the development of ageing research in solid organ transplantation, which can fully develop the potential of elderly organs and reduce the age gap between demand and supply. We conclude that the main characteristics of cellular senescence, the anti-ageing drug senolytics in the treatment of chronic diseases and organ transplantation, and the latest clinical progress of related researches in order to provide a theoretical basis for the prevention and treatment of ageing and related diseases.

Ultrasensitive electrochemical microRNA-21 detection based on MXene and ATRP photocatalytic strategy.

A Ti3C2TxMXene-based biosensor has been developed and the photocatalytic atom transfer radical polymerization (photo ATRP) amplification strategy applied to detect target miRNA-21 (tRNA). Initially, Ti3C2TxMXene nanosheets were synthesized from the Ti3AlC2 MAX precursor via selective aluminum etching. Then, functionalization of Ti3C2TxMXene nanosheets with 3-aminopropyl triethoxysilane (APTES) via silylation reactions to facilitate covalent bonding with hairpin DNA biomolecules specifically designed for tRNA detection. Upon binding with the tRNA, the hairpin DNA liberated the azide (N3) group, initiating a click reaction to affix to the photo ATRP initiator. Through the ATRP photoreaction, facilitated by an organic photoredox catalyst and light, a significant amount of ferrocenyl methyl methacrylate (FMMA) monomer was immobilized on the electrode. Therefore, the electrochemical signal is amplified. The electrochemical efficacy of the biosensor was assessed using square wave voltammetry (SWV). Under optimized conditions, the biosensor demonstrated remarkable sensitivity in detecting tRNA, with a linear detection range from 0.01 fM to 10 pM and a detection limit of 2.81 aM. The findings elucidate that the developed biosensor, in conjunction with the photo ATRP strategy, offers reproducibility, stability, and increased sensitivity, underscoring its potential applications within the experimental medical sector of the biomolecular industry.

Ferritin-Enhanced Direct MicroRNA Detection via Controlled Radical Polymerization.

Accurate quantitative detection of tracing nucleic acids remains a great challenge in cancer genetic testing. It is crucial to propose a low-cost and highly sensitive direct gene detection method for cancer prevention and treatment. Herein, this work reports an ultrasensitive biosensor via a ferritin-enhanced atom-transfer radical polymerization (Ft-ATRP) process. Intriguingly, microRNA-21, an early marker of lung cancer, can be detected without being transcribed in advance by an innovative signal amplification strategy using ferritin-mediated aggregation of hydrophilic nitroxide radical monomers as an electrochemical biosensor. The sensor uses peptide nucleic acid probes modified on a gold electrode to accurately bind the target lung cancer marker in the sample, and then ferritin, which is naturally present in human blood, induces Ft-ATRP on the electrode surface under mild conditions. Many of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine 1-oxyl free radical (MATMP) monomers with electrochemical signals are combined into polymeric chains to be modified on target assays. The limit of detection (LOD) of microRNA-21 is as low as 6.03 fM, and the detection concentration ranges from 0.01 to 100 pM (R2 = 0.994). The RNA biosensor can realize great performance analysis of complicated samples in simple operation, in addition, the detection process used by the catalyst, polymers containing electrochemical signals, and the electrolyte solution all have good water solubility. The superior performance of the RNA biosensor demonstrates its potential to screen and identify lung cancer in target patients.

Cyanocobalamin (VB12) Bionic Enzyme-Assisted Photocatalytic Chain-Growth Polymerization for Detection of Lung Cancer Biomarkers.

Cobalt-mediated radical polymerization is noted for its great level of control over the polymerization of acrylic and vinyl esters monomers, even at high molar mass. Vitamin B12, a natural bionic enzyme cobalt complex, involves the conversion of organic halides to olefins through chain-growth polymerization. In this work, the notion of R-Co(III) free radical persistent free radical effect and vitamin B12 circulation were first reported for the perception of ultralow abundance of microRNA-21, a lung cancer biomarker. Indeed, most Co-containing catalytic reactions can occur under mild conditions due to their minimal bond dissociation of the C-Co bond, with blue light irradiation. Based on the intrinsic stability of the vitamin B12 framework and recycling of the catalyst, it is evident that this natural catalytic scheme has potential applications in medicinal chemistry and biomaterials. In addition, this strategy, combined with highly specific recognition probes and vitamin B12 circulation-mediated chain-growth polymerization, has a detection limit as low as 910 aM. Furthermore, it is sensitive for sensing in serum samples containing biomarkers and shows great potential for RNA selection and amplification sensing in clinical samples.

Sensitive electrochemical detection of A549 exosomes based on DNA/ferrocene-modified single-walled carbon nanotube complex.

Exosome is an emerging tumor marker, whose concentration level can reflect the occurrence and development of tumors. The development of rapid and sensitive exosome detection platform is of great significance for early warning of cancer occurrence. Here, a strategy for electrochemical detection of A549-cell-derived exosomes was established based on DNA/ferrocene-modified single-walled carbon nanotube complex (DNA/SWCNT-Fc). DNA/SWCNT-Fc complexes function as a signal amplification platform to promote electron transfer between electrochemical signal molecules and electrodes, thereby improving sensitivity. At the same time, the exosomes can be attached to DNA/SWCNT-Fc nanocomposites via the established PO43--Ti4+-PO43- method. Moreover, the application of EGFR antibody, which can specifically capture A549 exosomes, could improve the accuracy of this sensing system. Under optimal experimental conditions, the biosensor showed good linear relationship between the peak current and the logarithm of exosomes concentration from 4.66 × 106 to 9.32 × 109 exosomes/mL with a detection limit of 9.38 × 104 exosomes/mL. Furthermore, this strategy provides high selectivity for exosomes of different cancer cells, which can be applied to the detection of exosomes in serum samples. Thus, owing to its advantages of high sensitivity and good selectivity, this method provides a diversified platform for exosomes identification and has great potential in early diagnosis and biomedical applications.

A dichromatic plasmonic ELISA CD81 protein sensor for ultrasensitive detection of preeclampsia.

Preeclampsia (PE) seriously affects pregnant women and fetuses' health and causes maternal near-misses. CD81 has been confirmed to be a novel PE biomarker with great potential. Herein, a hypersensitive dichromatic biosensor based on the plasmonic enzyme-linked immunosorbent assay (plasmonic ELISA) is proposed initially for the application of CD81 in early screening for PE. In this work, a novel chromogenic substrate [(HAuCl4)-(N-methylpyrrolidone)-(Na3C6H5O7)] is designed based on the H2O2 dual catalysis reduction pathway of Au ions. The two reduction pathways of Au ions are controlled by H2O2 which ensures that the synthesis and growth of AuNPs are sensitive to H2O2. The amount of H2O2 correlates with the concentration of CD81 and directs the production of different-sized AuNPs in this sensor. Blue solutions are generated when analytes are present. When analytes are absent, solutions turn red. Therefore, due to different absorption peaks in red and blue, bimodal detection can be performed, and then two detection signals can be generated, one on signal at 550 nm and another off signal at 600 nm. This method exhibits a linear response to the logarithmic CD81 concentrations in the range of 0.1-1000 pg mL-1 with detection limits of 86 fg mL-1 and 152 fg mL-1 at two wavelengths. The false positive rate is low due to the nonspecific coloration caused by serum, which produces a more intense color contrast. The results indicate that the proposed dichromatic sensor could be used as a visual sensing platform for the direct detection of CD81 in biological samples and demonstrate its potential in preeclampsia diagnosis.

Mn-MOF catalyzed multi-site atom transfer radical polymerization electrochemical sensing of miRNA-21.

A green electrochemical biosensor was developed based on metal-organic framework (MOF)-catalyzed atom transfer radical polymerization (ATRP) for quantifying miRNA-21, used as the proof-of-concept analyte. Unlike conventional ATRP, Mn-PCN-222 (PCN, porous coordination network) could be used as an alternative for green catalyst to substitute traditional catalysts. First, poly (diallyldimethylammonium chloride) (PDDA) was fixed on the surface of the indium tin oxide (ITO) electrode, and then the Mn-PCN-222 was linked to ITO electrode via electrostatic binding with PDDA. Next, aminated ssDNA (NH2-DNA) was used to modify the electrode further by amide reaction with Mn-PCN-222. Then, the recognition and hybridization of NH2-DNA with miRNA-21 prompt the generation of DNA-RNA complexes, which further hybridize with Fc-DNA@ß-CD-Br15 and permit the initiator to be immobilized on the electrode surface. Accordingly, ß-CD-Br15 could initiate the polymerization of ferrocenylmethyl methacrylates (FcMMA) under the catalysis of MOF to complete the ATRP reaction. FcMMA presented a distinct electrochemical signal at ~ 0.33 V. Taking advantage of the unique multi-site properties of ß-CD-Br15 and the efficient catalytic reaction induced by Mn-PCN-222, ultrasensitive detection of miRNA-21 was achieved with a detection limit of 0.4 fM. The proposed electrochemical biosensor has been applied to the detection of miRNA-21 in serum samples. Therefore, the proposed strategy exhibited potential in early clinical biomedicine.

Fluorescent assay of alkaline phosphatase activity via atom transfer radical polymerization.

A novel fluorescence assay is proposed through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) strategy for alkaline phosphatase (ALP) activity detection. First of all, 2-bromo-2-methylpropionic acid (BMP) was employed as the initiator to modify on the surface of the magnetic nanoparticle (Fe3O4-MNP) by amide bonding. Then, ascorbic acid (AA) produced by ALP catalyzed the phosphate group removal from L-ascorbic acid 2-phosphate sesquimagnesium salt hydrate (AAPS), which underwent a redox reaction with Cu(II) and the product Cu(I) triggered the ARGET ATRP reaction. Finally, a strong fluorescent signal could be detected at 514 nm due to numerous fluorescent monomers being grafted to the Fe3O4-MNPs surface (Ex = 490 nm, Em = 514 nm). Under optimal experimental conditions, the linear range of this fluorometric assay for ALP activity was 1-80 mU mL-1, and the detection limit was 0.68 mU mL-1. The method exhibited excellent selectivity and satisfactory results were obtained in the inhibition rate and human serum experiments. Therefore, this ALP activity detection strategy has great potential for clinically relevant disease detection and drug screening. A novel fluorescence strategy for alkaline phosphatase activity detection based on the dephosphorylation property of alkaline phosphatase and ARGET ATRP reaction.

Application of peptide nucleic acid in electrochemical nucleic acid biosensors.

The early diagnosis of major diseases, such as malignant tumors, has always been an important field of research. Through screening, early detection of such diseases, and timely and effective treatment can significantly improve the survival rate of patients and reduce medical costs. Therefore, the development of a simple detection method with high sensitivity and strong specificity, and that is low cost is of great significance for the diagnosis and prognosis of the disease. Electrochemical DNA biosensing analysis is a technology based on Watson Crick base complementary pairing, which uses the capture probe of a known sequence to specifically recognize the target DNA and detect its concentration. Because of its advantages of low cost, simple operation, portability, and easy miniaturization, it has been widely researched and has become a cutting-edge topic in the field of biochemical analysis and precision medicine. However, the existing methods for electrochemical DNA biosensing analysis have some shortcomings, such as poor stability and specificity of capture probes, insufficient detection sensitivity, and long detection cycles. In this review, we focus on improving the sensitivity and practicability of electrochemical DNA biosensing analysis methods and summarize a series of research work carried out by using electrically neutral peptide nucleic acid as an immobilized capture probe.

A Highly Selective and Sensitive Peptide-Based Fluorescent Ratio Sensor for Ag.

A fluorescence ratio sensor based on dansyl-peptide, Dansyl-Glu-Cys-Glu-Glu-Trp-NH2 (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. The sensor exhibits high selectivity and sensitivity for Ag+ over 16 metal ions in 100 mM sodium perchlorate and 50 mM 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid buffer solution by fluorescence resonance energy transfer. The 1:1 binding stoichiometry of the sensor and Ag+ is measured by fluorescence ratio response and the job's plot. The dissociation constant of the sensor with Ag+ was calculated to be 6.4 × 10-9 M, which indicates that the sensor has an effective binding affinity for Ag+. In addition, the limit of detection of the sensor for Ag+ was determined to be 80 nM, which also indicates that the sensor has a high sensitivity to Ag+. Result showed that the sensor is an excellent Ag+ sensor under neutral condition. Furthermore, this sensor displays good practicality for Ag+ detection in river water samples without performing tedious sample pretreatment, as well as for silver chloride detection.

Electrochemical ultrasensitive detection of CYFRA21-1 using Ti3C2Tx-MXene as enhancer and covalent organic frameworks as labels.

The concentration level of cytokeratin fragment antigen 21-1 (CYFRA21-1) can be used as an important indicator for predicting non-small cell lung cancer (NSCLC). Here, a sandwich-type electrochemical immunosensor for ultrasensitive detection of CYFRA21-1 is developed. The sensor based on a combination of gold nanoparticle (AuNPs) decorated Ti3C2Tx-MXene (Au-Ti3C2Tx) as the substrate enhancer, and toluidine blue (TB) modified AuNPs doped covalent organic framework (COF) polymer as the signal tag (TB-Au-COF). The Au-Ti3C2Tx is used to capture numerous primary antibodies and accelerate the electron transfer rate of the substrate, while the TB-Au-COF can be applied to provide a large number of signal units TB and secondary antibodies. These features of composites endow the proposed immunosensor with high sensitivity and current response to CYFRA21-1. Under optimum conditions, the immunosensor offers a wide current response for CYFRA21-1 from 0.5-1.0 × 104 pg·mL-1 with a detection limit of 0.1 pg·mL-1. Furthermore, the biosensing platform can be applied for CYFRA21-1 detection to analyze real serum samples, providing an effective and useful avenue for the applicability of Au-Ti3C2Tx and TB-Au-COF composite materials in biosensing field.

Functionalized graphene oxide in situ initiated ring-opening polymerization for highly sensitive sensing of cytokeratin-19 fragment.

Improving the sensitivity of detection is crucial to monitor biomarker, assess toxicity, and track therapeutic agent. Herein, a sensitivity-improved immunosensor is reported for the first time via functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy. Through the ROP reaction using 2-[(4-ferrocenylbutoxy)methyl] oxirane (FcEpo) as the monomer, lots of electroactive tags are linked in situ from multiple initiation sites on the GO surface modified with ethanol amine (GO-ETA), thereby achieving high sensitivity even in the case of trace amounts of tumor markers. The utmost important factor for achieving this high sensitivity is to select functionalized GO as the initiator that contains a large number of repeated hydroxyl functional groups so as to trigger additional ROP reaction. Under the optimal conditions, the high sensitivity and applicability is demonstrated by the use of GO-ETA-mediated ROP-based immunosensor to detect non-small cell lung cancer (NSCLC)-specific biomarker down to 72.58 ag/mL (equivalent to ~6 molecules in a 5 µL sample). Furthermore, the satisfactory results for the determination of biomarkers in clinical serum samples highlighted that this immunosensor holds a huge potential in practical clinical application. This work described an electrochemical immunosensor for ultrasensitive detection of CYFRA 21-1 via the functionalized graphene oxide (GO) and a "grafting-to" ring-opening polymerization (ROP) dual signal amplification strategy, which hold the merits of high sensitivity, applicability, selectivity, efficiency, easy operation and environmental friendliness.

Metal-Free Photoinduced Atom Transfer Radical Polymerization for Highly Sensitive Detection of Lung Cancer DNA.

Convenient and sensitive detection of biomolecules is of great significance to disease diagnosis. In this work, a metal-free photoinduced atom transfer radical polymerization (photoATRP) by a reductive quenching pathway as a novel strategy is applied to achieve lung cancer DNA detection. Thiolated PNA is exploited to specifically recognize target DNA, and the initiator of photoATRP is linked to the electrode surface via phosphate-Zr4+ -carboxylate. Under the excitation of blue light, the reductive quenching pathway is activated with eosin Y (EY) as photoredox catalyst and N,N,N',N'',N'-pentamethyldiethylenetriamine (PMDETA) as electron donor, and numerous polymeric chains are formed. Under optimal conditions, the linear range of this strategy is from 0.1 pm to 10 nm (R2 =0.989) with a limit of detection (LOD) of 1.4 fm (14 zmol in 10 µL). The variety of possible light sources for photoATRP and simple operation endow this biosensor with great potential for practical applications.

Intramolecular photoinitiator induced atom transfer radical polymerization for electrochemical DNA detection.

A novel electrochemical biosensor was reported for the first time to achieve highly sensitive DNA detection based on photoinduced atom transfer radical polymerization (photoATRP). In this work, PNA was applied as the capture probe to specifically recognize the target DNA (TDNA), and we utilized lung cancer DNA as TDNA. The ATRP initiator was introduced to the electrode surface via phosphate-Zr4+-carboxylate chemistry. PhotoATRP was activated under blue light irradiation based on a photoinitiator I2959, which produced free radicals via homolytic cleavage. Subsequently, Cu2+ was reduced to Cu+ with the assistance of the free radicals, and numerous electroactive probes were grafted onto the electrode surface. Under optimal conditions, the limit of detection (LOD) of this method was 3.16 fM (S/N = 3, R2 = 0.992), and the linear range was from 10 fM to 1.0 nM. More importantly, the preparation process of this biosensor was simple and less laborious with a low background signal, suggesting good potential in practical applications.

Polysaccharide-enhanced ARGET ATRP signal amplification for ultrasensitive fluorescent detection of lung cancer CYFRA 21-1 DNA.

An ultrasensitive fluorescence biosensor for detecting cytokeratin fragment antigen 21-1 (CYFRA 21-1) DNA of non-small cell lung carcinoma (NSCLC) is designed using polysaccharide and activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) signal amplification strategy. Thiolated peptide nucleic acid (PNA) is fixed on magnetic nanoparticles (MNPs) by a cross-linking agent and hybridized with CYFRA 21-1 DNA. Hyaluronic acid (HA) is linked to PNA/tDNA heteroduplexes in the form of carboxy-Zr4+-phosphate. Subsequently, multiple 2-bromo-2-methylpropionic acid (BMP) molecules are linked with HA to initiate ARGET ATRP reaction. Finally, a large number of fluorescein o-acrylate (FA) monomers are polymerized on the macro-initiators, and the fluorescence signal is significantly amplified. Under optimal conditions, this biosensor shows a significant linear correlation between the fluorescence intensity and logarithm of CYFRA 21-1 DNA concentration (0.1 fM to 0.1 nM), and the limit of detection is as low as 78 aM. Furthermore, the sensor has a good ability to detect CYFRA 21-1 DNA in serum samples and to recognize mismatched bases. It suggests that the strategy has broad application in early diagnosis by virtue of its high sensitivity and selectivity. Graphical abstract A novel and highly sensitive fluorescence biosensor for quantitatively detecting CYFRA 21-1 DNA via dual signal amplification of hyaluronic acid and ARGET ATRP reaction was developed. This proposed method has a low detection limit, wide detection range, high selectivity, and strong anti-interference.

Electrochemical CYFRA21-1 DNA sensor with PCR-like sensitivity based on AgNPs and cascade polymerization.

In this work, a new method of CYFRA21-1 DNA (tDNA) detection based on electrochemically mediated atom transfer radical polymerization (e-ATRP) and surface-initiated reversible addition-fragmentation chain transfer polymerization (SI-RAFT) cascade polymerization and AgNP deposition is proposed. Firstly, the peptide nucleic acid (PNA) probe is captured on a gold electrode by Au-S bonds for specific recognition of tDNA. After hybridization, PNA/DNA strands provide high-density phosphate groups for the subsequent ATRP initiator by the identified carboxylate-Zr4+-phosphate chemistry. Then, a large number of monomers are successfully grafted from the DNA through the e-ATRP reaction. After that, the chain transfer agent of SI-RAFT and methacrylic acid (MAA) are connected by recognized carboxylate-Zr4+-carboxylate chemistry. Subsequently, through SI-RAFT, the resulting polymer introduces numerous aldehyde groups, which could deposit many AgNPs on tDNA through silver mirror reaction, causing significant amplification of the electrochemical signal. Under optimal conditions, this designed method exhibits a low detection limit of 0.487 aM. Moreover, the method enables us to detect DNA at the level of PCR-like and shows high selectivity and strong anti-interference ability in the presence of serum. It suggests that this new sensing signal amplification technology exhibits excellent potential of application in the early diagnosis of non-small cell lung cancer (NSCLC). Graphical abstract Electrochemical detection principle for CYFRA21-1 DNA based on e-ATRP and SI-RAFT signal amplification technology.

Electrochemically Controlled RAFT Polymerization for Highly Sensitive Electrochemical Biosensing of Protein Kinase Activity.

Phosphorylation of proteins catalyzed by protein kinases (PKs) is essential to many biological processes; the sensitive detection of PK activity and the screening of PK inhibitors are thus integral to disease diagnosis and drug discovery. Herein, a highly sensitive biosensor has been fabricated for the electrochemical detection of PK activity by exploiting the electrochemically controlled reversible addition-fragmentation chain transfer (eRAFT) polymerization as a novel amplification strategy. The fabrication of the eRAFT-polymerization-based electrochemical biosensor involves (1) the immobilization of substrate peptides onto a gold electrode by way of gold-sulfur self-assembly, (2) the site-specific phosphorylation of substrate peptides by PKs, (3) the anchoring of carboxyl-group-containing chain transfer agents (CTAs) to the phosphorylated sites, and (4) the eRAFT polymerization under a potentiostatic condition, using ferrocenylmethyl methacrylate (FcMMA) as the monomer. Through the eRAFT polymerization, long polymer chains containing numerous electroactive Fc tags can be de novo grafted from each phosphorylated site, resulting in significant amplification of the electrochemical detection signal. The as-fabricated biosensor is highly selective and features a very low detection limit of 1.02 mU mL-1, in the presence of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent PK (PKA) as the model target. Results also demonstrate that it can be applied to the screening of PK inhibitors and the detection of PK activity in complex serum samples and cell lysates. Moreover, it holds the merits of easy fabrication, high efficiency, and low cost, which make it a promising tool for the detection of PK activity and the screening of potential PK inhibitors.

Ultrasensitive Detection of DNA via SI-eRAFT and in Situ Metalization Dual-Signal Amplification.

In this work, we report a new amplification strategy based on electrochemically mediated reversible addition-fragmentation chain transfer (eRAFT) and in situ metalization for electrochemical detection of DNA. First, peptide nucleic acid (PNA) probes were immobilized on the surface of the gold electrode, and when they hybridized with the target DNA, the chain transfer agent (CTA), 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD), of RAFT was connected to the PNA/DNA heteroduplex formed by the coordination bonding of Zr4+. Then glycosyloxyethyl methacrylates (GEMA) were assembled on the surface of the electrode by electrochemically mediated surface-initiated reversible addition-fragmentation chain transfer (SI-eRAFT) to form a polymer-containing sugar glucose. Next, the o-hydroxyl groups on the polysaccharide molecular skeleton were oxidized to aldehyde groups by sodium periodate (NaIO4). The aldehyde groups generated then reduce silver ions to silver particles deposited on the electrode surface in situ, and this system was then subjected to differential pulse voltammetry (DPV). Under optimal conditions, the intensity of the stripping current and the logarithm of the target DNA (tDNA) concentration has a good linear relationship in the range of 10 aM to 1 pM (R2 = 0.996), and the detection limit can go down to 5.4 aM (S/N = 3). Moreover, the method is suitable for single-nucleotide polymorphism (SNP) analysis and has strong anti-interference ability for the analysis of target ssDNA in serum samples.

An electrochemical aptasensor based on eATRP amplification for the detection of bisphenol A.

Herein, a novel aptasensor was constructed for ultrasensitive detection of bisphenol A (BPA). In this method, an electrochemically mediated atom transfer radical polymerization (eATRP) signal amplification strategy was applied to BPA detection for the first time. The 5'-end modified sulfhydryl group and the 3'-end modified azide group hairpin DNA were immobilized on a gold electrode through an Au-S bond. The double-stranded DNA was formed by the hybridization of an aptamer and a single-stranded DNA partially paired with the hairpin DNA. In the presence of BPA, the aptamer combined with BPA and the single-stranded DNA was released to open the hairpin structure, making the azide groups at the 3' end exposed. Subsequently the initiator of eATRP was introduced into hairpin DNA through click chemistry reaction and eATRP was conducted for the polymerization of the electroactive probe ferrocene methyl methacrylate (FMMA). As a result, the ultrasensitive detection of BPA was realized, and the detection limit of this aptasensor was as low as 59 aM and a good selectivity was obtained in the presence of 100-fold structural analogs. The application of this aptasensor was evaluated by detecting BPA in pure water samples, and recoveries were in the range of 95.23-98.40%, holding promising applications in biological analysis.