Aggregation of Individual Sensing Units for Signal Accumulation: Conversion of Liquid-Phase Colorimetric Assay into Enhanced Surface-Tethered Electrochemical Analysis

Review of nanomaterial advances for ionizing radiation dosimetry

There are a wide range of applications with ionizing radiation and a common theme throughout these is that accurate dosimetry is usually required, although many newer demands are provided by improved features in higher range, multi-spectral and particle type detected. Today, the array of dosimeters includes both offline and online tools, such as gel dosimeters, thermoluminescence (TL), scintillators, optically stimulated luminescence (OSL), radiochromic polymeric films, gels, ionization chambers, colorimetry, and electron spin resonance (ESR) measurement systems. Several future nanocomposite features and interpretation of their substantial behaviors are discussed that can lead to improvements in specific features, such as (1) lower sensitivity range, (2) less saturation at high range, (3) overall increased dynamic range, (4) superior linearity, (5) linear energy transfer and energy independence, (6) lower cost, (7) higher ease of use, and (8) improved tissue equivalence. Nanophase versions of TL and ESR dosimeters and scintillators each have potential for higher range of linearity, sometimes due to superior charge transfer to the trapping center. Both OSL and ESR detection of nanomaterials can have increased dose sensitivity because of their higher readout sensitivity with nanoscale sensing. New nanocrystalline scintillators, such as perovskite, have fundamentally important advantages in sensitivity and purposeful design for key new applications. Nanoparticle plasmon coupled sensors doped within a lower Zeff material have been an effective way to achieve enhanced sensitivity of many dosimetry systems while still achieving tissue equivalency. These nanomaterial processing techniques and unique combinations of them are key steps that lead to the advanced features. Each must be realized through industrial production and quality control with packaging into dosimetry systems that maximize stability and reproducibility. Ultimately, recommendations for future work in this field of radiation dosimetry were summarized throughout the review.

Surface-tethered electrochemical biosensor for telomerase detection by integration of homogeneous extension and hybridization reactions

The general electrochemical biosensors for telomerase detection require the immobilization of primers on the electrode surface for telomeric extension and hybridization reactions. However, immobilization of primers may suffer from the challenges of hindrance effect and configuration freedom, thus reducing the extension and hybridization efficiency. Herein, we developed a sensitive electrochemical biosensor for telomerase detection by integration of homogeneous extension and hybridization reactions and surface-tethered detection. In the presence of telomerase, the biotinylated primer (bio-primer) was efficiently elongated with telomeric repeats of (TTAGGG)_n at the 3' end in solution. Then, the extension product (bio-DNA) was hybridized with the signal probe DNA modified on the surface of ferrocene (Fc)-capped gold nanoparticle (AuNP). The bio-DNA/DNA/Fc-AuNP hybrids were then tethered by streptavidin-modified electrodes through the specific avidin-biotin interactions, thus producing strong electrochemical signals from the oxidation of Fc tags. The biosensor was successfully used to determine telomerase in HeLa cells and monitor the inhibition efficiency of inhibitor. A wide linear range for the detection of telomerase extracted from HeLa cells was attained. This method has great potential in clinical diagnosis and anti-cancer drug development, and should be beneficial for the fabrication of novel biosensors by integration of homogeneous catalysis and hybridization reactions.

Recent Progress in Nanotechnology-Based Approaches for Food Monitoring

Throughout the food supply chain, including production, storage, and distribution, food can be contaminated by harmful chemicals and microorganisms, resulting in a severe threat to human health. In recent years, the rapid advancement and development of nanotechnology proposed revolutionary solutions to solve several problems in scientific and industrial areas, including food monitoring. Nanotechnology can be incorporated into chemical and biological sensors to improve analytical performance, such as response time, sensitivity, selectivity, reliability, and accuracy. Based on the characteristics of the contaminants and the detection methods, nanotechnology can be applied in different ways in order to improve conventional techniques. Nanomaterials such as nanoparticles, nanorods, nanosheets, nanocomposites, nanotubes, and nanowires provide various functions for the immobilization and labeling of contaminants in electrochemical and optical detection. This review summarizes the recent advances in nanotechnology for detecting chemical and biological contaminations in the food supply chain.

A nucleic acid dye-enhanced electrochemical biosensor for the label-free detection of Hg2+ based on a gold nanoparticle-modified disposable screen-printed electrode

In this paper, a nucleic acid dye-enhanced electrochemical biosensor based on a screen-printed carbon electrode (SPCE) modified with Au nanoparticles (AuNPs) was designed for the detection of Hg²⁺ in water. AuNPs were modified on the surface of the disposable SPCE through the electrodeposition of HAuCl₄. Subsequently, thiolated DNA probes were immobilized on the AuNP-modified electrode surface by Au-S reaction. After Hg²⁺ was bound with a DNA probe by thymine (T)-Hg²⁺-thymine (T) mismatch, the DNA probe was folded into a hairpin structure where positively charged GelRed molecules were embedded into the double-stranded part of the hairpin. Thus, the current of [Fe(CN)₆]^3-/4- increased significantly on account of the decreased electrostatic repulsion at the electrode surface. Under the optimized experimental conditions, the peak current of [Fe(CN)₆]^3-/4- exhibited a good linear relationship with lgC_Hg²⁺ in the concentration of Hg²⁺ linear range of 0.1 nM to 500 nM, and the limit of detection (S/N = 3) was calculated as 0.04 nM. The electrochemical sensor also exhibited excellent selectivity for Hg²⁺ in the presence of nine interfering ions, including Na⁺, Fe³⁺, Ni²⁺, Mg²⁺, Co²⁺, Pb²⁺, K⁺, Al³⁺ and Cu²⁺. Meanwhile, the developed electrochemical sensor was tested in the analysis of Hg²⁺ in tap water and river water samples, and the recoveries ranged from 81.0 to 114%. Therefore, this nucleic acid dye-enhanced electrochemical biosensor provided the advantages of simplicity, sensitivity, and specificity and is expected to be an alternative for Hg²⁺ detection in actual environmental samples.

Colorimetric and Electrochemical Methods for the Detection of SARS-CoV-2 Main Protease by Peptide-Triggered Assembly of Gold Nanoparticles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro) has been regarded as one of the ideal targets for the development of antiviral drugs. The currently used methods for the probing of Mpro activity and the screening of its inhibitors require the use of a double-labeled peptide substrate. In this work, we suggested that the label-free peptide substrate could induce the aggregation of AuNPs through the electrostatic interactions, and the cleavage of the peptide by the Mpro inhibited the aggregation of AuNPs. This fact allowed for the visual analysis of Mpro activity by observing the color change of the AuNPs suspension. Furthermore, the co-assembly of AuNPs and peptide was achieved on the peptide-covered electrode surface. Cleavage of the peptide substrate by the Mpro limited the formation of AuNPs/peptide assembles, thus allowing for the development of a simple and sensitive electrochemical method for Mpro detection in serum samples. The change of the electrochemical signal was easily monitored by electrochemical impedance spectroscopy (EIS). The detection limits of the colorimetric and electrochemical methods are 10 and 0.1 pM, respectively. This work should be valuable for the development of effective antiviral drugs and the design of novel optical and electrical biosensors.

Surface-enhanced Raman spectroscopy and density functional theory study of thymine-1-acetic acid interaction with silver nanoparticles

Thymine-1-acetic acid (TAA) is a modified nucleobase often used to add thymine functionality to materials. This study reports the Raman band assignments for TAA by comparing its experimental and density functional theory (DFT) simulated Raman spectra. Further comparison of experimental surface-enhanced Raman spectroscopy (SERS) of TAA on silver nanoparticles (Ag NPs) with simulated spectra of various complexes of xAg+ (x = 1, 2, or 3) and TAA reveals its likely adsorption orientation on the Ag NPs. This is one of the few studies that has achieved reasonably accurate simulation of SERS by employing multiple unconnected Ag+ ions, which could represent a compromise between a single atom or ion on one hand and a computationally expensive cluster on the other.

In Situ Assembly of Nanomaterials and Molecules for the Signal Enhancement of Electrochemical Biosensors

The physiochemical properties of nanomaterials have a close relationship with their status in solution. As a result of its better simplicity than that of pre-assembled aggregates, the in situ assembly of nanomaterials has been integrated into the design of electrochemical biosensors for the signal output and amplification. In this review, we highlight the significant progress in the in situ assembly of nanomaterials as the nanolabels for enhancing the performances of electrochemical biosensors. The works are discussed based on the difference in the interactions for the assembly of nanomaterials, including DNA hybridization, metal ion-ligand coordination, metal-thiol and boronate ester interactions, aptamer-target binding, electrostatic attraction, and streptavidin (SA)-biotin conjugate. We further expand the range of the assembly units from nanomaterials to small organic molecules and biomolecules, which endow the signal-amplified strategies with more potential applications.

Ultrasensitive detection of trace Hg2+ by SERS aptasensor based on dual recycling amplification in water environment

Due to the nonbiodegradability and accumulation of mercury ion, even in extremely small amount, it will cause varying degrees of harm to environment and human health. Although researchers have developed many strategies to detect and monitor trace Hg²⁺, only a few provide sensitivities of less than 1.0 pM. Surface Enhanced Raman Spectroscopy (SERS) is a common method to detect mercury ion due to its high sensitivity, rapid detection and easy operation. In this work, we report a new SERS aptasensor based on dual recycling amplification for the detection of trace mercury ion, which combines SERS with nucleic acid signal amplification through functional aptamer and elaborately designed hairpin DNA. Under the optimal experimental conditions, this SERS aptasensor exhibits excellent selectivity and high sensitivity. A linear range (0.2-125 fM) and a low detection limit (0.11 fM) are obtained. By using specific aptamers, the strategy will provide a new idea for the trace detection of toxic contaminants in water environment.

Fluorometric discrimination of tyrosine isomers based on the inner filter effect of chiral Au nanoparticles on MoS2 quantum dots

A fluorescent chiral sensor is proposed based on the inner filter effect (IFE) of chiral Au nanoparticles (AuNPs) on MoS2 quantum dots (MoS2 QDs), which can be used for the discrimination of the isomers of tyrosine (Tyr). l-Tyrosine (l-Tyr) can induce obvious agglomeration of the chiral AuNPs, leading to an attenuated IFE of the chiral AuNPs and greatly restored fluorescence of the MoS2 QDs, and thus the enantioselective recognition of the Tyr isomers can be achieved. Also, l-Tyr but not d-Tyr induced agglomeration of the chiral AuNPs is confirmed by the larger association constant between l-Tyr and the chiral sensor.

A versatile switchable dual-modal colorimetric and photoelectrochemical biosensing strategy via light-controlled sway of a signal-output transverter

A design criterion to construct a versatile dual-modal colorimetric and PEC biosensing platform for switching the corresponding mode freely is proposed via integration of a natural enzyme, light-activated nanozyme and light-controlled swayable signal-output transverter. A switchable dual-modal platform toward DNA analysis is developed as a proof of concept.

Silver nanoparticle driven signal amplification for electrochemical chiral discrimination of amino acids

β-Cyclodextrin (β-CD) modified silver nanoparticles (AgNPs), denoted as β-CD/AgNPs, were prepared by a simple one-pot method. Due to the inherent chirality of β-CD, the developed β-CD/AgNPs exhibited higher affinity toward l-tyrosine (l-Tyr) than d-tyrosine (d-Tyr), leading to serious aggregation of AgNPs in the presence of l-Tyr. Consequently, the l-Tyr induced aggregation of AgNPs can result in signal amplification in the differential pulse voltammograms (DPVs) of l-Tyr, which can be applied for the electrochemical chiral discrimination of the Tyr enantiomers. Other chiral amino acids including tryptophan and phenylalanine can also be successfully discriminated with the β-CD/AgNPs, suggesting high universality of the developed chiral sensor.

Thymine-Functionalized Gold Nanoparticles (Au NPs) for a Highly Sensitive Fiber-Optic Surface Plasmon Resonance Mercury Ion Nanosensor

Mercury ion (Hg²⁺) is considered to be one of the most toxic heavy metal ions. Once the content of Hg²⁺ exceeds the quality standard in drinking water, the living environment and health of human beings will be threatened and destroyed. Therefore, the establishment of simple and efficient methods for Hg²⁺ ion detection has important practical significance. In this paper, we present a highly sensitive and selective fiber-optic surface plasmon resonance (SPR) Hg²⁺ ion chemical nanosensor by designing thymine (T)-modified gold nanoparticles (Au NPs/T) as the signal amplification tags. Thymine-1-acetic acid (T-COOH) was covalently coupled to the surface of 2-aminoethanethiol (AET)-modified Au NPs and Au film by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride/N-Hydroxysuccinimide (EDC/NHS) activation effect, respectively. In the presence of Hg²⁺ ions, the immobilized thymine combines specifically with Hg²⁺ ions, and forms an Au/thymine-Hg²⁺-thymine/Au (Au/T-Hg²⁺-T/Au) complex structure, leading to a shift in SPR wavelength due to the strong electromagnetic couple between Au NPs and Au film. Under optimal conditions, the proposed sensor was found to be highly sensitive to Hg²⁺ in the range of 80 nM–20 µM and the limit of detection (LOD) for Hg²⁺ was as low as 9.98 nM. This fiber-optic SPR sensor afforded excellent selectivity for Hg²⁺ ions against other heavy metal ions such as Fe³⁺, Cu²⁺, Ni²⁺, Ba²⁺, K⁺, Na⁺, Pb²⁺, Co²⁺, and Zn²⁺. In addition, the proposed sensor was successfully applied to Hg²⁺ assay in real environmental samples with excellent recovery. Accordingly, considering its simple advantages, this novel strategy provides a potential platform for on-site determination of Hg²⁺ ions by SPR sensor.

Coordination of Ligand-Protected Metal Nanoclusters and Glass Nanopipettes: Conversion of a Liquid-Phase Fluorometric Assay into an Enhanced Nanopore Analysis

We propose a unique concept for transforming the liquid-phase fluorometric assay into an enhanced nanopore analysis, which is based on the analyte binding-mediated changes in the surface chemistry of noble metal nanostructures in a confined space. In a proof-of-concept trial, the bovine serum albumin-protected gold nanoclusters (BSA-Au NCs) were designed as the sensing unit for biothiol determination. Through the specific interaction between biothiols and BSA-Au NCs, the validation system not only performed well in aqueous fluorescent detection but also can be developed into a more selective and sensitive nanopore sensor. In the confined space of the nanopore, the BSA-Au NC film with high density formed, and the addition of biothiols triggered the fluorescence enhancement as well as the ionic current response, hence leading to the construction of the dual-signal-output (fluorescence/ion current signal) system. The fluorescence signal proved that the ionic current change corresponded to the specific recognition process, improving the reliability of our nanopore method. Moreover, the ionic current response from the BSA-Au NC film can be used to quantify cysteine in a broad dynamic range of 0.001-1 pM with a detection limit as low as 1 fM. Such a strategy can be used to detect biothiols in complex biological fluids such as human serum. Therefore, the present work provided a new design strategy for a glass nanopipette sensor inspired by the principles of numerous and diverse fluorometric assays. It also sheds light on how the coupling of electrical and optical signals improves the accuracy, sensitivity, and selectivity of the glass nanopipette platform.

Dual-Color Plasmonic Nanosensor for Radiation Dosimetry

Radiation dosimeters are critical for accurately assessing the levels of radiation exposure of tumor sites and surrounding tissues and for optimizing therapeutic interventions as well as for monitoring environmental exposure. To fill the need for a simple, user-friendly, and inexpensive dosimeter, we designed an innovative colorimetric nanosensor-based assay for detecting ionizing radiation. We show that hydroxyl radicals generated by ionizing radiation can be used to etch gold nanorods (AuNRs) and silver nanoprisms (AgNPRs), yielding reproducible color changes for radiation dose detection in the range of 50-2000 rad, broad enough to cover doses used in hyperfractionated, conventional, and hypofractionated radiotherapy. This range of doses detected by this assay correlates with radiation-induced DNA damage response in mammalian cells. Furthermore, this AuNR- and AgNPR-based sensing platform has been established in a paper format that can be readily adopted for a wide range of applications and translation.

Modification-free amperometric biosensor for the detection of wild-type p53 protein based on the in situ formation of silver nanoparticle networks for signal amplification

Sensitive and accurate quantification of wild-type p53 protein is of great importance for biological research and clinical diagnosis. Herein, a modification-free amperometric biosensor was proposed for sensitive detection of wild-type p53 protein by the signal amplification of silver nanoparticles (AgNPs) networks formed in situ on electrode surface. Double-stranded DNA (dsDNA) probe containing two consensus sites was immobilized on gold electrode surface to capture wild-type p53 protein. The cysteine thiol and amine groups on the exterior of the protein allowed for the attachment of bare AgNPs through the AgS or AgN interactions. Meanwhile, benzene-1,4-dithiol (BDT) molecules in solution triggered the assembly of more AgNPs on electrode surface through the AgS interactions, thus leading to the in situ formation of AgNPs networks for signal amplification. The target at the concentration as low as 0.1 pM can be readily determined. This method was further applied to determine wild-type p53 protein in spiked human serum and cell lysates with satisfactory results. Moreover, the biosensor is regenerative and does not require the modification of AgNPs with recognition element for signal readout. The modification-free strategy can potentially be applied to develop novel biosensors for detection of other biological macromolecules.

Ratiometric assay of mercury ion based on nitrogen-doped carbon dots with two different optical signals: second-order scattering and fluorescence

Ratiometric assays, which can effectively surmount external interference, have attracted extensive research interests. Herein, a novel ratiometric sensing platform for Hg²⁺ is designed based on nitrogen-doped carbon dots (N-CDs) with two different optical signals. Under a single excitation, N-CDs have two emission peaks around 668 nm and 412 nm, which are second-order scattering and fluorescence, respectively. Upon the addition of Hg²⁺, the weak scattering emission at 668 nm can be increased apparently, while the strong fluorescence intensity at 412 nm is weakened. Moreover, the ratio of scattering intensity to fluorescence intensity is linearly dependent on Hg²⁺ concentration (0.1-10 μM and 10-30 μM, respectively), and the detection limit is 66 nM. In addition, the ratiometric sensing mechanism is investigated in detail, which is due to the combined effect of aggregation-induced fluorescence quenching and scattering enhancement. Furthermore, the developed sensing approach holds a promising application for Hg²⁺ detection in actual samples. Graphical abstract.

A dendritically amplified fluorescent signal probe on SiO2 microspheres for the ultrasensitive detection of mercury ions

In this work, a new kind of dendritically amplified fluorescent signal probe on SiO₂ microspheres was controllably fabricated by the terminal deoxynucleotidyl transferase (TdT)-catalyzed incorporation of nucleotides combined with bio-barcode (BBC) amplification for the ultrasensitive detection of Hg²⁺. A thymine T-Hg²⁺-T hairpin structure was first formed and further initiated the strand displacement amplification (SDA) reaction, generating a mimic target (MT). MT hybridized with a capture probe 1 (C1) on SiO₂ microspheres, and the 3'-hydroxyl (OH) termini of MT initiated TdT-based DNA extension, producing abundant poly-guanine sequences (G1). Then, G1 hybridized with a capture probe 2 (C2) with abundant cytosine (C) species to assemble multiple C2/reporter probe-AuNPs onto the SiO₂ microspheres. The reporter DNA further initiated TdT-based extension with a poly-T sequence (T1) to link large numbers of signal probes, which generated a very high fluorescence signal for the ultrasensitive detection of target Hg²⁺. This TdT-based signal amplification method coupled with SDA exhibits extraordinary sensitivity for Hg²⁺ assay with a limit down to 1.0 aM. The proposed highly sensitive fluorescence strategy holds great potential for detecting targets in environmental and biological fields.

Simply translating mercury detection into a temperature measurement: using an aggregation-activated oxidase-like activity of gold nanoparticles

A new household thermometer-based POCT analysis for mercury based on the aggregation-activated oxidase-like activity of gold nanoparticles.

A simple thermometer-based photothermometric assay for alkaline phosphatase activity based on target-induced nanoprobe generation

Alkaline phosphatase (ALP)-induced in situ generation of Prussian blue nanoparticles for photothermometric ALP detection.

Interface engineering of microelectrodes toward ultrasensitive monitoring of β-amyloid peptides in cerebrospinal fluid in Alzheimer's disease

Aβ monomers directed the assembly of Cu²⁺-PEI/AuNPs-hemin nanoprobes into network aggregates on a microelectrode interface for enhanced electrochemical analysis.

Acetylcholinesterase-catalyzed silver deposition for ultrasensitive electrochemical biosensing of organophosphorus pesticides

This work reports, for the first time, acetylcholinesterase-catalyzed silver deposition for sensitive electrochemical detection of organophosphorus pesticides.

Colorimetric Assay Conversion to Highly Sensitive Electrochemical Assay for Bimodal Detection of Arsenate Based on Cobalt Oxyhydroxide Nanozyme via Arsenate Absorption

This study reports a novel and convenient bimodal method for label-free and signal-off detection of arsenate in environmental samples. Cobalt oxyhydroxide (CoOOH) nanoflakes with facile preparation and intrinsic peroxidase-like activity as nanozyme can efficiently catalyze the conversion of chromogenic substrate such as 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with the presence of H₂O₂ into green-colored oxidation products. CoOOH nanoflakes can specifically bind with arsenate via electrostatic attraction and As-O bond interaction, which gives rise to inhibition of the peroxidase-like activity of CoOOH. Thus, through arsenate specific inhibition of CoOOH nanozyme toward ABTS catalysis, a simple colorimetric method was developed for arsenate detection with a detection limit of 3.72 ppb. Based on the system of CoOOH nanozyme and ABTS substrate, this colorimetric method can be converted into an electrochemical sensor for arsenate assay by the utilization of CoOOH nanoflake-modified electrode. The electrochemical measurement can be realized by chronoamperometry, which showed more sensitive and a lower limit of detection as low as 56.1 ppt. The applicability of this bimodal method was demonstrated by measuring arsenate and total arsenic in different real samples such as natural waters and soil extracted solutions, and the results are of satisfactory accuracy as confirmed by inductively coupled plasma mass spectrometry analysis. The bimodal strategy offers obvious advantages including a label-free step, convenient operation, on-site assay, low cost, and high sensitivity, which is promising for reliable detection of arsenate and total arsenic in environmental samples.

Target-induced diffusivity enhancement for rapid and highly sensitive homogeneous electrochemical detection of BLM in human serum

A simple, rapid, and sensitive homogeneous electrochemical bleomycin (BLM) bioassay has been successfully developed through the target-induced specific/efficient cleavage reaction. The designed probe, denoted as MB-DNA, contains both methylene blue (MB) and target recognizable sequences, and presents relatively low electrochemical signal. Upon the addition of BLM, the recognition/cleavage reaction occurs and leads to the in-situ generation of MB tag (MB-DNA-1), leading to the reduced electrostatic repulsive force. As a result, an obvious enhancement in differential pulse voltammetry (DPV) current is determined, which is relied on the amount of BLM. Thus, a turn on homogeneous electrochemical method for BLM is really achieved, and exhibits high sensitivity of 33 pM, and the shortest response time of 20 min. Furthermore, this electrochemical bioassay presents excellent sensing performance in the analysis of BLM in real samples. Comparing with other sensing strategies for BLM, this proposed electrochemical platform is just consisted of one DNA probe alone, and affords a really rapid and sensitive strategy for BLM analysis.

Curvature-Mediated Surface Accessibility Enables Ultrasensitive Electrochemical Human Methyltransferase Analysis

The development of new tools for tracking the activity of human DNA methyltransferases is an important goal given the role of this enzyme as a cancer biomarker and epigenetic modulator. However, analysis of the human DNA (cytosine-5)-methyltransferase 1 (Dnmt1) activity is challenging, especially in crude samples, because of the low activity and large size of the enzyme. Here, we report a new approach to Dnmt analysis that combines nanostructured electrodes with a digest-and-amplify strategy that directly monitors Dnmt1 activity with high sensitivity. Nanostructured electrodes are required for the function of the assay to promote the accessibility of the electrode for human Dnmt1. Moreover, DNA-templated deposition of silver nanoparticles (for signal amplification) is combined with DNA Exonuclease I digestion to yield optimal target-to-control signals. We achieve high sensitivity for the detection of human Dnmt1, and particularly Dnmt1 from crude cell lysates. Specifically, the detection limit of our electrochemical assay is 20 pM, which is 2 orders of magnitude lower than previously reported methods. In crude lysates, we detected Dnmt1 from as few as five colorectal cancer cells (HCT116). With biopsy samples, we were able to distinguish colorectal tumor tissue from healthy adjacent tissue using only 10 μg of sample. The strategy enables analysis of an important marker underlying the epigenetic basis of cancerous transformation.

An electric potential modulated cascade of catalyzed hairpin assembly and rolling chain amplification for microRNA detection

MicroRNAs serve as a new type of biomarker for multifarious diseases due to its critical roles in post transcriptional gene regulation. Herein, we firstly integrate the catalyzed hairpin assembly (CHA) and rolling circle amplification (RCA) into an electrochemical biosensor for sensitive and specific detection of miR-21. Meanwhile, an electric potential was employed to modulate the efficiency of CHA occurred on the electrode, which offer a simple but effective method to surmount the accessibility problem of probes. The biosensor achieved an ultrasensitive determination of miR-21 with a low limit of detection of 13.5 fM and a linear range from 15 fM to 250 pM. This research encourages us to challenge the hyphenated multiple amplification strategies and provides a stable and effective method for the detection of diseases-related miRNAs in peripheral biofluids, as well as paves a road for the future clinical diagnostics and treatment of disease.

Fluorescence Regulation of Copper Nanoclusters via DNA Template Manipulation toward Design of a High Signal-to-Noise Ratio Biosensor

Because of bioaccumulation of food chain and disability of biodegradation, concentration of toxic mercury ions (Hg²⁺) in the environment dramatically varies from picomolar to micromolar, indicating the importance of well-performed Hg²⁺ analytical methods. Herein, reticular DNA is constructed by introducing thymine (T)-Hg²⁺-T nodes in poly(T) DNA, and copper nanoclusters (CuNCs) with aggregate morphology are prepared using this reticular DNA as a template. Intriguingly, the prepared CuNCs exhibit enhanced fluorescence. Meanwhile, the reticular DNA reveals evident resistance to enzyme digestion, further clarifying the fluorescence enhancement of CuNCs. Relying on the dual function of DNA manipulation, a high signal-to-noise ratio biosensor is designed. This analytical approach can quantify Hg²⁺ in a very wide range (50 pM to 500 μM) with an ultralow detection limit (16 pM). Besides, depending on the specific interaction between Hg²⁺ and reduced l-glutathione (GSH), this biosensor is able to evaluate the inhibition of GSH toward Hg²⁺. In addition, pollution of Hg²⁺ in three lakes is tested using this method, and the obtained results are in accord with those from inductively coupled plasma mass spectrometry. In general, this work provides an alternative way to regulate the properties of DNA-templated nanomaterials and indicates the applicability of this way by fabricating an advanced biosensor.

Cucurbituril and Azide Cofunctionalized Graphene Oxide for Ultrasensitive Electro-Click Biosensing

To achieve high selectivity and sensitivity simultaneously in an electrochemical biosensing platform, cucurbituril and azide cofunctionalized graphene oxide, a new functional nanomaterial that acts as a go-between to connect the recognition element with amplified signal architecture, is developed in this work. The cucurbituril and azide cofunctionalized graphene oxide features a high specific surface area with abundant levels of the two types of functional groups. Specifically, it emerges as a powerful tool to link recognition elements with simplicity, high yield, rapidity, and highly selective reactivity through azide-alkynyl click chemistry. Moreover, it possesses many host molecules to interact with guest molecules (also signal molecules)-grafted branched ethylene imine polymer, through which the detection sensitivity can be greatly improved. Together with electro-click technology, a highly controllable, selective, and sensitive biosensing platform can be easily created. For VEGF₁₆₅ protein detection, the electro-click assay has high selectivity and sensitivity; a dynamic detection range from 10 fg mL^-1 to 1 ng mL^-1 with a detection limit of 8 fg mL^-1 was achieved. The electro-click biosensing strategy based on cucurbituril and azide cofunctionalized graphene oxide would have great promise for other target analytes with a broad range of applications.

Poly-cytosine-mediated nanotags for SERS detection of Hg2

Highly sensitive and selective detection of heavy metal ions, such as Hg²⁺, is of great importance because the contamination of heavy metal ions has been a serious threat to human health. Herein, we have developed poly-cytosine (polyC)-mediated surface-enhanced Raman scattering (SERS) nanotags as a sensor system for rapid, selective, and sensitive detection of Hg²⁺ based on thymidine-Hg²⁺-thymidine (T-Hg²⁺-T) coordination and polyC-mediated Raman activity. The SERS nanotags exploit the mismatched T-T base pairs to capture Hg²⁺ form T-Hg²⁺-T bridges, which induce the aggregation of nanotags giving rise to the drastic amplification in the SERS signals. Moreover, this polyC not only provides the anchoring function to induce the formation of intrinsic silver-cytosine coordination but also engineers the Raman-activity of SERS nanotags by mediating its length. As a result, the polyC-mediated SERS nanotags show an excellent response for Hg²⁺ in the concentration range from 0.1 to 1000 nM and good selectivity over other metal ions. Given its simple principle and easy operation, the polyC-mediated SERS nanotags, therefore, could serve as a promising sensor for practical use.

Integrated amplified aptasensor with in-situ precise preparation of copper nanoclusters for ultrasensitive electrochemical detection of microRNA 21

MicroRNA 21 (MIR21) has garnered much attention in recent years as an important disease biomarker. The detection of it in human system shows great significance for the healthy evaluation and major diseases early detection. Herein, a novel approach tactfully manipulates the in-situ precise preparation of copper nanoclusters on overlapping Y-shaped ds-DNA for MIR21 analysis were developed in the proposed integrated aptasensor. In the presence of target MIR21, overlapping Y-shaped ds-DNA was constructed on electrode. Copper nanoclusters were in-situ prepared on this effective template for target detection. Taking advantage of exonuclease T7 triggered targets recycling, hybridization chain reaction (HCR) and copper nanoclusters triple amplification strategy, linear detection of MIR21 was achieved from 10pM to 0.1fM with a detection limit down to 10aM (S/N > 3). This approach provides a good model for integrating both synthesis and detection into one electrochemistry component. It showed promising potential for applications in aptamer related target detection in human serum analysis.