Amplified electrochemiluminescence detection of DNA-binding protein based on the synergy effect of electron and energy transfer between CdS nanocrystals and gold nanoparticles

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.

Shell-Isolated Nanoparticle-Enhanced Electrochemiluminescence

Enhanced electrochemiluminescence (ECL) aims to promote higher sensitivity and obtain better detection limit. The core-shell nanostructures, owing to unique surface plasmon resonance (SPR) enabling distance-dependent strong localized electromagnetic field, have attracted rising attention in enhanced ECL research and application. However, the present structures usually with porous shell involve electrocatalytic activity from the metal core and adsorption effect from the shell, which interfere with practical SPR enhancement contribution to ECL signal. Herein, to exclude the interference and unveil exact SPR-enhanced effect, shell-isolated nanoparticles (SHINs) whose shell gets thicker and becomes pinhole-free are developed by modifying pH value and particles concentration. Furthermore, allowing for the distribution of hotspots and stronger enhancement, excitation intensity and ECL reaction layer thickness are mainly investigated, and several types of SHINs-enhanced ECL platforms are prepared to fabricate distinct hotspot distribution via electrostatic attraction (submonolayer) and a layer-by-layer deposition method (monolayer). Consequently, the strongest enhancement up to ≈250-fold is achieved by monolayer SHINs with 10 nm shell, and the platform is applied in a "turn-off" mode sensing for dopamine. The platform provides new guidelines to shell preparation, interface engineering and hotspots fabrication for superior ECL enhancement and analytical application with high performance.

A novel label-free solid-state electrochemiluminescence sensor based on the resonance energy transfer from Ru(bpy)32+ to GO for DNA hybridization detection

Based on electrochemiluminescence resonance energy transfer (ERET) from Ru(bpy)₃²⁺ to graphene oxide (GO), a novel label-free solid-state ECL sensor for sensitive detection of DNA was proposed. First, Ru(bpy)₃²⁺/AuNPs was successfully prepared by using a simple and green method and characterized by transmission electron microscopy (TEM), Energy Dispersive X-ray (EDX), and UV-vis spectroscopy. Then, the Ru(bpy)₃²⁺/AuNPs colloid was assembled on the gold electrode surface for solid-state ECL film which also later could be used to immobilize thiol-derivatized, single-stranded DNA (HS-ssDNA) via Au-S interactions. The stepwise modification procedure was characterized by cyclic voltammetry(CV), electrochemical impedance spectroscopy (EIS), probe approach curves (PAC) and ECL, respectively. The resulting modified electrode was tested as ECL biosensor for DNA detection. Upon addition of GO, the strong noncovalent interaction between HS-ssDNA and GO led to ECL quenching because of ERET. When in the presence of target ssDNA (t-ssDNA), the distance between the HS-ssDNA and GO increased, which significantly hindered the ERET and, thus, resulted in the restoration of ECL. The ECL intensity of the biosensor increased linearly with t-ssDNA concentration in the range of 50-1000pM, and the detection limit is 20pM. To the best of our knowledge, this is the first application of solid-state ERET from Ru(bpy)₃²⁺ to GO and opens new opportunities for sensitive detection of biorecognition events.

A gold nanocluster chemical tongue sensor array for Alzheimer's disease diagnosis

Alzheimer's disease (AD) is a common neurodegenerative disorder in elderly people, and is associated with a heavy financial burden on our society. The use of serologic biomarkers is an attractive method to diagnose AD. Although the determination of blood-based biomarkers for AD has been explored in many studies, few practical diagnosis methods have been used in the clinic. In this work, we constructed a "chemical tongue" sensor array that is easy to use and based on four kinds of fluorescent gold nanoclusters (Au NCs) for discriminating between multiple proteins at nanomolar concentrations. The device utilizes a linear discrimination analysis based on fluorescence intensity response patterns. Using this chemical tongue sensor array, multiple proteins can be confidently identified even in complex biological systems, such as human urine. Most importantly, sera of AD patients could be effectively discriminated from those of osteoarthritis patients, or of healthy people. Also, the results obtained for the AD patients by the chemical tongue sensor array were validated by CSF determination. We conclude that the chemical tongue sensor array manufactured in this work paves the way for designing an auxiliary diagnosis method for AD that is less invasive and more convenient for the large-scale screening of patients.

Modified fractal iron oxide magnetic nanostructure: A novel and high performance platform for redox protein immobilization, direct electrochemistry and bioelectrocatalysis application

A novel biosensing platform based on fractal-pattern of iron oxides magnetic nanostructures (FIOMNs) and mixed hemi/ad-micelle of sodium dodecyl sulfate (SDS) was designed for the magnetic immobilization of hemoglobin (Hb) at a screen printed carbon electrode (SPCE). The FIOMNs was successfully synthesized through hydrothermal approach and characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). In order to provide guidelines for the mixed hemi/ad-micelle formation, zeta-potential isotherms were investigated. The construction steps of the biosensor were evaluated by electrochemical impedance spectroscopy, cyclic voltammetry and Fourier transform infrared spectroscopy. Direct electron transfer of Hb incorporated into the biocomposite film was realized with a pair of quasi-reversible redox peak at the formal potential of -0.355V vs. Ag/AgCl attributing to heme Fe(III)/Fe(II) redox couple. The results suggested that synergistic functions regarding to the hyper-branched and multidirectional structure of FIOMNs and the dual interaction ability of mixed hemi/ad-micelle array of SDS molecules not only induce an effective electron transfer between the Hb and the underlying electrode (high heterogeneous electron transfer rate constant of 2.08s(-1)) but also provide powerful and special microenvironment for the adsorption of the redox proteins. Furthermore, the biosensor displayed an excellent performance to the electrocatalytic reduction of H2O2 with a detection limit of 0.48µM and Michaelis-Menten constant (Km) value of 44.2µM. The fabricated biosensor represented the features of sensitivity, disposable design, low sample volume, rapid and simple preparation step, and acceptable anti-interferences, which offer great perspectives for the screen-determination of H2O2 in real samples.

Tellurium platinate nanowires for photothermal therapy of cancer cells

Among the most celebrated modes of cancer treatment, photothermal therapy has been the most promising tool over the past few years.

Silver Nanoclusters for High-Efficiency Quenching of CdS Nanocrystal Electrochemiluminescence and Sensitive Detection of microRNA

In this work, oligonucleotide-encapusulated silver nanoclusters were applied in the electrochemiluminescence (ECL) system of CdS nanocrystals (NCs)/ K2S2O8 based on dual ECL quenching effects. We found that the ECL emission of CdS NCs matched well with the absorption band of oligonucleotide encapsulated Ag nanoclusters, which could act as the energy acceptor of CdS NCs ECL so as to lead to an effective ECL resonance energy transfer (RET). On the other hand, the Ag nanoclusters could also catalyze electrochemical reduction of K2S2O8, resulting in increased consumption of ECL coreactant near the working electrode and decreased ECL intensity from CdS NCs. On the basis of the dual ECL quenching effects, a sensitive ECL biosensor for detection of microRNA was successfully achieved with a wide linear range from 10 fM to 100 pM.

Label-free and enzyme-free detection of transcription factors with graphene oxide fluorescence switch-based multifunctional G-quadruplex-hairpin probe

Transcription factors (TFs) play pivotal roles in the regulation of a variety of essential cellular processes and some of them have been recognized as potential diagnostic markers and therapeutic targets of some diseases. Sensitive and accurate detection of TFs is of great importance to better understanding their roles in gene regulation and evaluation of disease state. Here, we developed a simple, label-free and enzyme-free new fluorescent strategy for the detection of TFs by graphene oxide (GO) fluorescence switch-based multifunctional G-quadruplex-hairpin probe (MGHP). The MGHP possessed of three functions simultaneously, adsorbing onto GO with the loop part, binding to target with the stem part and serving as signal carrier with the terminal G-quadruplex. First, the MGHP was adsorbed quickly to GO. Next, the TF bound to the stem part of MGHP to form a huge target-MGHP complex, which led to desorption of the complex from GO. Finally, NMM was inserted into G-quadruplex in the complex to yield an enhanced fluorescence response. The GO used here, as a fluorescence switch, could quickly and efficiently quench the fluorescence of NMM inserted into the MGHP absorbed on the GO, guaranteeing a high signal-to-noise ratio. Sensitive detection of purified NF-κB p50 and HeLa cell nuclear extracts were achieved with detection limits of 0.2nM and 7.8ng/µL, respectively. Moreover, this proposed strategy could be used to screen inhibitors of NF-κB p50 activity. The strategy proposed here might offer a new potential approach for reliable quantification of TFs in clinical diagnostics and treatment research of some diseases.

A novel electrochemiluminescent immunosensor based on CdS-coated ZnO nanorod arrays for HepG2 cell detection

In this work, the highly oriented CdS-coated-ZnO nanorod arrays have been fabricated. The CdS-coated-ZnO nanorod arrays show high electrochemiluminescence intensity, fast response and good stability. All of the desirable properties spur the development of an ECL immunosensor for the detection of the liver cancer cell line (HepG2 cells). Two successive modification steps of 3-aminopropyltriethoxysilane and gold nanoparticles onto the CdS-coated-ZnO nanorod arrays not only offer the substrates for conjugation of antibody, but also effectively enhance the ECL signal, resulting in production of the high performance ECL immunosensor. The ECL immunosensor exhibits a sensitive response to HepG2 cells in a linear range of 300-10,000 cells mL(-1) with a detection limit of 256 cells mL(-1). The proposed sensor characteristics of high specificity, good reproducibility and remarkable stability will provide a sensitive, selective, and convenient approach for the clinical detection of cancer cells.

Integration of DNA bio-gates and duplex-specific nuclease signal amplification: towards electrochemiluminescence detection of survivin mRNA

Based on the integration of DNA bio-gates and duplex-specific nuclease assisted target recycling, a facile electrochemiluminescence assay was developed for the sensitive detection of survivin mRNA.

A new visible-light-driven photoelectrochemical biosensor for probing DNA–protein interactions

A novel photoelectrochemical approach was achieved for the detection of a DNA binding protein via the protein–DNA interaction.

Horseradish peroxidase immobilization on carbon nanodots/CoFe layered double hydroxides: direct electrochemistry and hydrogen peroxide sensing

Carbon nanodots and CoFe layered double hydroxide composites (C-Dots/LDHs) were prepared via simply mixing C-Dots and CoFe-LDHs. The as-prepared composites were used for the immobilization of horseradish peroxidase (HRP) on the glass carbon (GC) electrode. The electrochemical behavior of the HRP/C-Dots/LDHs/GC electrode and its application as a H2O2 biosensor were investigated. The results indicated that HRP immobilized by C-Dots/LDHs retained the activity of enzyme and displayed quasi-reversible redox behavior and fast electron transfer with an electron transfer rate constant ks of 8.46 s(-1). Under optimum experimental conditions, the HRP/C-Dots/LDHs/GC electrode displayed good electrocatalytic reduction activity and excellent analytic performance toward H2O2. The H2O2 biosensor showed a linear range of 0.1-23.1 μM (R(2) = 0.9942) with a calculated detection limit of 0.04 μM (S/N = 3). In addition, the biosensor exhibited high sensitivity, good selectivity, acceptable reproducibility and stability. The superior properties of this biosensor are attributed to the synergistic effect of HRP, C-Dots and CoFe-LDHs, which has been proved by investigating their electrochemical response to H2O2. Thus the C-Dots and LDHs composites provide a promising platform for the immobilization of redox enzymes and construction of sensitive biosensors.

An off-on-off electrochemiluminescence approach for ultrasensitive detection of thrombin

This work demonstrates an aptasensor for ultrasensitive electrochemiluminescence (ECL) detection of thrombin based on an "off-on-off" approach. The system is composed of an Eu(3+)-doped CdS nanocrystals (CdS:Eu NCs) film on glassy carbon electrode (GCE) as ECL emitter. Then gold nanoparticles (AuNPs) labeled hairpin-DNA probe (ssDNA1) containing thrombin-binding aptamer (TBA) sequence was linked on the NCs film, which led to ECL quenching (off) as a result of Förster-resonance energy transfer (FRET) between the CdS:Eu NC film and the proximal AuNPs. Upon the occurrence of hybridization with its complementary DNA (ssDNA2), an ECL enhancement (on) occurred owing to the interactions of the excited CdS:Eu NCs with ECL-induced surface plasmon resonance (SPR) in AuNPs at large separation. Thrombin could induce ssDNA1 forming a G-quadruplex and cause the AuNPs to be close to CdS:Eu NCs film again, which resulted in an enhanced ECL quenching (off). This "off-on-off" system showed a maximum 7.4-fold change of ECL intensity due to the configuration transformation of ssDNA1 and provides great sensitivity for detection of thrombin in a wide detection range from 50 aM to 1 pM.

Sensitive detection of transcription factors using an Ag+-stabilized self-assembly triplex DNA molecular switch

A simple, enzyme-free and sensitive new fluorescent strategy for detection of transcription factors was proposed based on a bifunctional Ag⁺-stabilized self-assembly triplex DNA molecular switch.