A highly selective and sensitive detection of insulin with chemiluminescence biosensor based on aptamer and oligonucleotide-AuNPs functionalized nanosilica @ graphene oxide aerogel

High-density microneedle array-based wearable electrochemical biosensor for detection of insulin in interstitial fluid

The development of point-of-care wearable devices capable of measuring insulin concentration has the potential to significantly improve diabetes management and life quality of diabetic patients. However, the lack of a suitable point-of-care device for personal use makes regular insulin level measurements challenging, in stark contrast to glucose monitoring. Herein, we report an electrochemical transdermal biosensor that utilizes a high-density polymeric microneedle array (MNA) to detect insulin in interstitial fluid (ISF). The biosensor consists of gold-coated polymeric MNA modified with an insulin-selective aptamer, which was used for extraction and electrochemical quantification of the insulin in ISF. In vitro testing of biosensor, performed in artificial ISF (aISF), showed high selectivity for insulin with a linear response between 0.01 nM and 4 nM (sensitivity of ∼65 Ω nM-1), a range that covers both the physiological and the pathological concentration range. Furthermore, ex vivo extraction and quantification of insulin from mouse skin showed no impact on the biosensor's linear response. As a proof of concept, an MNA-based biosensing platform was utilized for the extraction and quantification of insulin on live mouse skin. In vivo application showed the ability of MNs to reach ISF, extract insulin from ISF, and perform electrochemical measurements sufficient for determining insulin levels in blood and ISF. We believe that our MNA-based biosensing platform based on extraction and quantification of the biomarkers will help move insulin assays from traditional laboratory approaches to personalized point-of-care settings.

Graphene-Oxide Peptide-Containing Materials for Biomedical Applications

This review explores the application of graphene-based materials (GBMs) in biomedicine, focusing on graphene oxide (GO) and its interactions with peptides and proteins. GO, a versatile nanomaterial with oxygen-containing functional groups, holds significant potential for biomedical applications but faces challenges related to toxicity and environmental impact. Peptides and proteins can be functionalized on GO surfaces through various methods, including non-covalent interactions such as π-π stacking, electrostatic forces, hydrophobic interactions, hydrogen bonding, and van der Waals forces, as well as covalent bonding through reactions involving amide bond formation, esterification, thiol chemistry, and click chemistry. These approaches enhance GO's functionality in several key areas: biosensing for sensitive biomarker detection, theranostic imaging that integrates diagnostics and therapy for real-time treatment monitoring, and targeted cancer therapy where GO can deliver drugs directly to tumor sites while being tracked by imaging techniques like MRI and photoacoustic imaging. Additionally, GO-based scaffolds are advancing tissue engineering and aiding tissues' bone, muscle, and nerve tissue regeneration, while their antimicrobial properties are improving infection-resistant medical devices. Despite its potential, addressing challenges related to stability and scalability is essential to fully harness the benefits of GBMs in healthcare.

Low-temperature subcritical water dechlorination composites of waste PVC/coal fly ash with powerful sensing activity for chemiluminescent detection of acetamiprid and imidacloprid

Pesticide residues in agricultural products are serious threat to people's health. Real-time monitoring of pesticides residues in the environment and agricultural products posed challenges to sustainable methods with high analytical performance for pesticide detection. Herein, waste PVC/coal fly ash (the mass ratio of PVC and coal fly ash was 4:1) was dechlorinated in subcritical water at low temperature to achieve nearly 100 % dechlorination of PVC and obtain carbon-based composite materials (CM-Fe/Al/Si-dPVC) with strong sening activity. For CM-Fe/Al/Si-dPVC, CFe bonding resulted in strong electron migration, and nano/μm SiO2 and Al2O3 doping in the layered polyene C matrix provided large specific surface area, and silicon hydroxyl created good heterogeneous catalytic interfaces. CM-Fe/Al/Si-dPVC could strongly trigger luminol chemiluminescence (CL) reaction and produce intense CL signals. Neonicotinoid pesticides (acetamiprid and imidacloprid) bonded with CM-Fe/Al/Si-dPVC through coordination chelation and hydrogen bonding, which shielded the catalytic active site and increased the Fermi level of system, thus quenching CL reaction. Inspired by these, a cheap CL assay was constructed for detecting neonicotinoids combinations of acetamiprid and imidacloprid (NICs). The detection limits of NICs were 0.7 ng/L. Satisfactory recoveries were obtained for real agricultural products and environmental samples. The results of life cycle evaluation (LCA) revealed that the strategy had significantly small global warming potential (GWP). This work presented a sustainable method with environmental benefits for the detection of neonicotinoids, and also opened up new way for the recycling of organic solid wastes.

Trends on Aerogel-Based Biosensors for Medical Applications: An Overview

Aerogels are unique solid-state materials composed of interconnected 3D solid networks and a large number of air-filled pores. This structure leads to extended structural characteristics as well as physicochemical properties of the nanoscale building blocks to macroscale, and integrated typical features of aerogels, such as high porosity, large surface area, and low density, with specific properties of the various constituents. Due to their combination of excellent properties, aerogels attract much interest in various applications, ranging from medicine to construction. In recent decades, their potential was exploited in many aerogels' materials, either organic, inorganic or hybrid. Considerable research efforts in recent years have been devoted to the development of aerogel-based biosensors and encouraging accomplishments have been achieved. In this work, recent (2018-2023) and ground-breaking advances in the preparation, classification, and physicochemical properties of aerogels and their sensing applications are presented. Different types of biosensors in which aerogels play a fundamental role are being explored and are collected in this manuscript. Moreover, the current challenges and some perspectives for the development of high-performance aerogel-based biosensors are summarized.

Impact of nanotechnology on progress of flow methods in chemical analysis: A review

In evolution of instrumentation for analytical chemistry as crucial technological breakthroughs should be considered a common introduction of electronics with all its progress in integration, and then microprocessors which was followed by a widespread computerization. It is seems that a similar role can be attributed to the introduction of various elements of modern nanotechnology, observed with a fast progress since beginning of this century. It concerns all areas of the applications of analytical chemistry, including also progress in flow analysis, which are being developed since the middle of 20th century. Obviously, it should not be omitted the developed earlier and analytically applied planar structures like lipid membranes or self-assembled monolayers They had essential impact prior to discoveries of numerous extraordinary nanoparticles such as fullerenes, carbon nanotubes and graphene, or nanocrystalline semiconductors (quantum dots). Mostly, due to catalytic effects, significantly developed surface and the possibility of easy functionalization, their application in various stages of flow analytical procedures can significantly improve them. The application of new nanomaterials may be used for the development of new detection methods for flow analytical systems in macro-flow setups as well as in microfluidics and lateral flow immunoassay tests. It is also advantageous that quick flow conditions of measurements may be helpful in preventing unfavorable agglomeration of nanoparticles. A vast literature published already on this subject (e.g. almost 1000 papers about carbon nanotubes and flow-injection analytical systems) implies that for this reviews it was necessary to make an arbitrary selection of reported examples of this trend, focused mainly on achievements reported in the recent decade.

Wearable Insulin Biosensors for Diabetes Management: Advances and Challenges

We present a critical review of the current progress in wearable insulin biosensors. For over 40 years, glucose biosensors have been used for diabetes management. Measurement of blood glucose is an indirect method for calculating the insulin administration dosage, which is critical for insulin-dependent diabetic patients. Research and development efforts aiming towards continuous-insulin-monitoring biosensors in combination with existing glucose biosensors are expected to offer a more accurate estimation of insulin sensitivity, regulate insulin dosage and facilitate progress towards development of a reliable artificial pancreas, as an ultimate goal in diabetes management and personalised medicine. Conventional laboratory analytical techniques for insulin detection are expensive and time-consuming and lack a real-time monitoring capability. On the other hand, biosensors offer point-of-care testing, continuous monitoring, miniaturisation, high specificity and sensitivity, rapid response time, ease of use and low costs. Current research, future developments and challenges in insulin biosensor technology are reviewed and assessed. Different insulin biosensor categories such as aptamer-based, molecularly imprinted polymer (MIP)-based, label-free and other types are presented among the latest developments in the field. This multidisciplinary field requires engagement between scientists, engineers, clinicians and industry for addressing the challenges for a commercial, reliable, real-time-monitoring wearable insulin biosensor.

Vanillin-Catalyzed highly sensitive luminol chemiluminescence and its application in food detection

Among various chemiluminescence (CL) systems, luminol-H₂O₂ system is used extensively due to its cheapness and sensitivity. Herein, 4-hydroxy-3-methoxybenzaldehyde, known as vanillin, was firstly found to be able to catalyze H₂O₂ very efficiently to produce ^•OH and O₂^•-, which can be used to enhance the CL of luminol-H₂O₂ as Co⁺. In alkaline aqueous solution, vanillin catalyzed the dissociation of H₂O₂ into active ^•OH and O₂^•- radicals and accelerated luminol-H₂O₂ reaction to emit strong CL signal. Combining the stabilizing function of β-CD, CL intensity of luminol-H₂O₂ was enhanced further. Thus, dual-signal amplification of luminol-H₂O₂ chemiluminescence based on the catalyzing function of vanillin and the stabilizing function of β-CD was proposed and its mechanism was explored deeply in the manuscript. Interestingly, vanillin is a highly prized flavor compound broadly used as food additive, however, the excessive intake of vanillin is harmful to human and thus the determination of vanillin is very important. On the basis of the luminol-β-CD-H₂O₂/vanillin reaction, a low-cost, rapid and simple CL sensor has been established to detect vanillin. The sensor was able to detect vanillin in the range of 1.0 μM ∼ 75 μM with a detection limit of 0.89 μM (S/N = 3). It can also be used for CL imaging detection with satisfactory results.

Controllable assembly of three-dimensional porous graphene-Au dual aerogels and its application for high-efficient bioelectrocatalytic O2 reduction

Aerogels derived from the colloidal nanoparticles featured with hierarchical interconnected pore-rich networks guarantee their great potentials in various applications. Herein, the controllable assembly of three-dimensional aerogels based on Au nanoparticles (Au NPs) and reduced graphene oxide (rGO) nanosheets as building blocks via a bottom-up approach have been systematically clarified. The difference of building blocks and their assembly sequence were crucially to the final aerogel morphologies and electrochemical properties. Specifically, the highly porous graphene-gold dual aerogels (rGO-Au DAGs) with interconnected rGO nanosheets and Au nanowires showed high conductivity, large surface area and good biocompatibility. Thus, it was employed as an excellent matrix to immobilize enzyme for high-efficient bioelectrocatalysis. Taking bilirubin oxidase as an example, a more positive on-set potential (0.60 V) and a larger catalytic current density (0.77 mA cm^-2@0.40 V) than those of other rGO-Au assemblies were achieved for direct bioelectrocatalytic O₂ reduction. This study will provide an efficient strategy for unique dual-structural aerogels design and shed light to develop new functional materials for bioelectrocatalytic applications such as biosensors and biofuel cells.

Capture and detection of Escherichia coli with graphene aerogels

Some pathogenic bacteria may cause serious food poisoning as well as catastrophic infections. Thus, it is critical to identify bacteria using simple, quick, and sensitive methods. Herein, we fabricate a graphene aerogel-based biosensing system to capture and detect Escherichia coli (E. coli) with high specificity and sensitivity. A graphene aerogel is prepared by a one-step hydrothermal synthesis method without any reducing reagent. With the help of E. coli antibodies and the graphene foam with a porous structure, E. coli can be captured using the detection substrate with high specificity and selectivity. The electrical resistance and electrochemical impedance spectroscopy (EIS) results of the graphene aerogel foam changed with high sensitivity during E. coli adhesion. Moreover, the resistance change of the graphene device can still be observed when the E. coli concentration was as low as 10 cfu mL^-1, while there is no obvious resistance change in the use of Staphylococcus aureus. The subsequent EIS test also found that the charge transfer resistance (R_ct) of the detection substrate gradually increased during the E. coli capture process. This nanoelectronic biosensor is simple, quick, safe, and very sensitive, and it may be used as a high-throughput platform for pathogenic bacterial detection, bacterial research, and antimicrobial drug screening.

Interference-resistant aptasensor with tetrahedral DNA nanostructure for profenofos detection based on the composites of graphene oxide and polyaniline

In this work, an interference-resistant electrochemical aptasensor that could detect profenofos in vegetables was constructed based on complexes of graphene oxide and polyaniline (GO@PANI) and gold nanoparticles-tetrahedral DNA nanostructure (Au-TDN). Compared with a single chain aptamer, the tetrahedral DNA nanostructure is highly stable and allows the aptamer on this structure to stand in a highly ordered position on an electrode surface. Moreover, the AuNPs are biocompatible and can protect the activity of the aptamer, which can improve the assembly success rate of Au-TDN. Besides, the conductivity of PANI had been tremendously enhanced thanks to the existence of GO, which improved the dispersion of PANI. The GO@PANI was prepared by a chemical synthesis method, which had a large surface area and was able to adsorb many Au-TDN. Under optimal working parameters, the constructed aptasensor exhibited good electrochemical sensing performance with a detection limit of 10.50 pg/mL and a linear range of 1.0 × 10²-1.0 × 10⁷ pg/mL. In addition, it was employed in detecting profenofos in vegetables with a good recovery rate of 90.41-116.37 %. More importantly, the aptasensor also has excellent stability and high selectivity. This study provides a promising method to avoid interference in the detection of profenofos by sensors.

A novel electrochemical insulin aptasensor: From glassy carbon electrodes to disposable, single-use laser-scribed graphene electrodes

Insulin, a peptide hormone secreted by pancreatic β cells, affects the development of diabetes and associated complications. Herein, we propose an electrochemical aptasensor for sensitive and selective detection of insulin using laser-scribed graphene electrodes (LSGEs). Before using disposable LSGEs, the development and proof-of-concept sensing experiments were firstly carried out on research-grade glassy carbon electrode (GCE). The aptasensor is based on using Exonuclease I (Exo I) that catalyses the hydrolysis of single-stranded aptamers attached to the electrode surface; however, the hydrolysis does not occur if the insulin is bound to the aptamer. Therefore, the unbound aptamers are cleaved by Exo I while insulin-bound aptamers remain on the electrode surface. In the next step, the gold nanoparticle - aptamer (AuNPs-Apt) probes are introduced to the electrode surface to form a 'sandwich' structure with the insulin on the surface-attached aptamer. The redox probe, methylene blue (MB), intercalates into the aptamers' guanine bases and the sandwich structure of AuNPs-Apt/insulin/surface-bound aptamer amplifies electrochemical signal from MBs. The signal can be well-correlated to the concentrations of insulin. A limit of detection of 22.7 fM was found for the LSGE-based sensors and 9.8 fM for GCE-based sensors used for comparison and initial sensor development. The results demonstrate successful fabrication of the single-use and sensitive LSGEs-based sensors for insulin detection.

Fabrication, Structure, Performance, and Application of Graphene-Based Composite Aerogel

Graphene-based composite aerogel (GCA) refers to a solid porous substance formed by graphene or its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), with inorganic materials and polymers. Because GCA has super-high adsorption, separation, electrical properties, and sensitivity, it has great potential for application in super-strong adsorption and separation materials, long-life fast-charging batteries, and flexible sensing materials. GCA has become a research hotspot, and many research papers and achievements have emerged in recent years. Therefore, the fabrication, structure, performance, and application prospects of GCA are summarized and discussed in this review. Meanwhile, the existing problems and development trends of GCA are also introduced so that more will know about it and be interested in researching it.

Au-quantum dot nanocluster electrochemiluminescence coupled with cycling-amplification for sensitive microRNA detection

A novel polyamidoamine (PAMAM) dendrimer-Au nanocluster composite was synthesized, and used to fabricate a new amplified electrochemiluminescence (ECL) signal probe for sensitive detection of microRNA by multiple strand displacement amplification (SDA) strategy. The as prepared PAMAM-Au nanocluster with many amino groups could assemble a large number of quantum dots (QDs) to greatly amplify ECL of the probe. In addition, a new sliver nanocluster (NC) with excellent conductivity and many reactive carboxyl groups was prepared, and used to immobilize a large amount of capture (c1) DNA molecules on the electrode. Moreover, by using bifunctional DNA strand displacement reaction-mediated multiple cycling-amplification technique, a small number of target miRNA could induce to generate abundant DNA (t1) fragments, which was used as a linker to hybridize with c1 DNA on the electrode, and then conjugate many amplified QDs probe. Thus an amplified ECL analytical method for detecting target miRNA was designed, and highly sensitive detection of miRNA was achieved. This newly established strategy paves a new way for homogeneous microRNA detection, which hold great potential for application in early clinical diagnosis.

2D Materials-Based Aptamer Biosensors: Present Status and Way Forward

Current advances in constructing functional nanomaterials and elegantly designed nanostructures have opened up new possibilities for the fabrication of viable field biosensors. Two-dimensional materials (2DMs) have fascinated much attention due to their chemical, optical, physicochemical, and electronic properties. They are ultrathin nanomaterials with unique properties such as high surface-to-volume ratio, surface charge, shape, high anisotropy, and adjustable chemical functionality. 2DMs such as graphene-based 2D materials, Silicate clays, layered double hydroxides (LDHs), MXenes, transition metal dichalcogenides (TMDs), and transition metal oxides (TMOs) offer intensified physicochemical and biological functionality and have proven to be very promising candidates for biological applications and technologies. 2DMs have a multivalent structure that can easily bind to single-stranded DNA/RNA (aptamers) through covalent, non-covalent, hydrogen bond, and π-stacking interactions, whereas aptamers have a small size, excellent chemical stability, and low immunogenicity with high affinity and specificity. This review discussed the potential of various 2D material-based aptasensor for diagnostic applications, e.g., protein detection, environmental monitoring, pathogens detection, etc.

An ultrasensitive electrochemical aptasensor based on a single-stranded aptamer-Au@Fe-MIL-88 complex using methylene blue as an electrochemical probe for insulin detection

This work introduces an electrochemical aptasensor based on a single-stranded aptamer-Au@Fe-MIL-88 complex for sensitive and selective determination of insulin using differential pulls voltammetry. Au@Fe-MIL-88 with a large surface area was synthesized and employed as a suitable substrate for immobilization of the aptamer (APT-Au@Fe-MIL-88). Methylene blue (MB), as an electrochemical probe, was intercalated into the aptamer. Graphene oxide (GO) and zinc sulfide (ZnS) were placed on the Au electrode to amplify the MB current. Also, ZnS improves the immobilization of APT-Au@Fe-MIL-88 into the aptasensor through the strong interaction of Au-S. In the presence of the insulin, MB is released from the aptamer due to DNA conformational change, and as a result, the peak intensity of the intercalated MB was decreased. Under optimal conditions, the change in the current of MB was proportional to the insulin concentration in the range of 5.0 × 10^-16-5.0 × 10^-11 mol L^-1, with a superior ultra-low detection limit of 1.3 × 10^-16 mol L^-1. It was observed that the aptasensor is suitable for determining insulin in serum samples with good sensitivity and reproducibility and with recoveries ranging from 96.4 to 102.0%. The relative standard deviations (RSD) were lower than 3.8% (n = 3).

Recent advances in the synthesis and applications of graphene-polypeptide nanocomposites

The combination of peptides and graphene-derived materials provides a new way to prepare graphene-based nanocomposites with unique structures, properties, and functions. The modification of graphene with different polypeptides not only improves the biocompatibility and biological recognition ability of graphene-based materials, but also greatly expands their application fields. In this work, we summarize different interactions between graphene and polypeptides, and the synthesis methods of novel functional graphene-polypeptide nanocomposites based on the interactions in recent years (from 2016 to present). In addition, the potential applications of graphene-peptide hybrid nanocomposites in biomedicine, tissue engineering, biosensors, environmental science engineering, optoelectronic materials, and energy storage are introduced. We hope that this review will help readers to understand the methods and mechanisms of the modification of graphene surfaces with biomolecules, and promote readers to understand the synthesis and applications of graphene-based nanocomposites. This work may provide hints and references for the development of peptide sequence design, and biomedical and functional materials, and will help in designing and synthesizing novel graphene-based nanomaterials with unique properties and suitable for various applications in the future.

Target-triggered and controlled release plasmon-enhanced fluorescent AIE probe for conformational monitoring of insulin fibrillation

In this work, we constructed a target-triggered and controlled-release plasmon-enhanced fluorescent AIE probe to realize the purpose of conformational monitoring of insulin fibrillation. We synthesized a novel water-soluble anthracene derivative, 4,4',4'',4'''-(anthracene-9,10-diylbis(ethene-2,1,1-triyl))tetrakis(N,N,N-trimethylbenzenaminium) iodide (BDVAI), with AIE properties, high biocompatibility and good self-assembly effect. Gold nanocages (AuNCs) were selected as the substrate for PEF, and the inner space of hollow AuNCs was filled with BDVAI. Thiol-modified DNA chains were bonded to the surface of AuNCs by Au-S bonds, and an insulin aptamer was combined with the sulfhydryl chain to seal the AuNCs. This PEF-AIE sensor produces different fluorescence signals when interacting with native insulin and fibrillar insulin; thus, monitoring conformational changes in insulin can be realized by detecting fluorescence intensity changes during insulin fibrillation. Based on this design, this system realized sensitive detection of fibrillar insulin with a detection limit of 23.6 pM. This AIE molecular-based PEF fluorescence enhancement system improves the optical properties of fluorescent substances, which is of great significance in improving the detection sensitivity of amyloid fibrils conformational changes and providing a reliable basis for further understanding the pathogenesis of amyloidosis.

Recent advances of functional nucleic acids-based electrochemiluminescent sensing

Electroluminescence (ECL) has been used in extensive applications ranging from bioanalysis to clinical diagnosis owing to its simple device requirement, low background, high sensitivity, and wide dynamic range. Nucleic acid is a significant theme in ECL bioanalysis. The inherent versatile selective molecular recognition of nucleic acids and their programmable self-assembly make it desirable for the robust construction of nanostructures. Benefiting from their unique structures and physiochemical properties, ECL biosensing based on nucleic acids has experienced rapid growth. This review focuses on recent applications of nucleic acids in ECL sensing systems, particularly concerning the employment of nucleic acids as molecular recognition elements, signal amplification units, and sensing interface schemes. In the end, an outlook of nucleic acid-based ECL biosensing will be provided for future developments and directions. We envision that nucleic acids, which act as an essential component for both bioanalysis and clinical diagnosis, will provide a new thinking model and driving force for developing next-generation sensing systems.

Paper-Based Bipolar Electrode Electrochemiluminescence Platform for Detection of Multiple miRNAs

This paper introduces a novel potential-resolved paper-based biosensor for simultaneous detection of multiple microRNAs (miRNAs) (taking miRNA-155 and miRNA-126 as examples) based on the bipolar electrode (BPE) electrochemiluminescence (ECL) strategy. The proposed multiple-channel paper-based sensing microfluidic platform was prepared by wax-printing technology, screen-printing method, and in situ Au nanoparticles (AuNPs) growth to form hydrophilic areas, hydrophobic boundaries, waterproof electronic bridge, driving electrode regions, and parallel bipolar electrode regions. CdTe quantum dots (QDs)-H2 and Au@g-C₃N₄ nanosheets (NSs)-DNA1 were used as dual electrochemiluminescence signal probes, and carboxylated Fe₃O₄ magnetic nanoparticles existed as carriers. CdTe QDs-H2/S₂O₈^2- and Au@g-C₃N₄ NSs-DNA1/S₂O₈^2- could exhibit two strong and stable ECL emissions at a drive voltage of 9 and 12 V, respectively, which can be used as effective potential-resolved signal tags. In addition, the proposed three-dimensional (3D) DNA nanomachine model and the target miRNA cycle strategy were used to achieve double amplification of electrochemiluminescence intensity. More importantly, the combination of the bipolar electrode system and the potential-resolved multitarget electrochemiluminescence method can greatly reduce the spatial interference between substances. The prepared ECL biosensor showed a favorable linear response for the detection of miRNA-155 and miRNA-126 with relatively low detection limits of 5.7 and 4.2 fM, respectively. With excellent sensitivity, the strategy may provide an efficient method for clinical application, especially in detection of trace multiple targets.

Nanomaterial-enhanced chemiluminescence reactions and their applications

Chemiluminescence (CL) analysis is a trace analytical method that possesses advantages including high sensitivity, wide linear range, easy operation, and simple instruments. With the development of nanotechnology, many nanomaterial (NM)-enhanced CL systems have been established in recent years and applied for the CL detection of metal ions, anions, small molecules, tumor markers, sequence-specific DNA, and RNA. This review summarizes the research progress of the nanomaterial-enhanced CL systems the past five years. These CL reactions include luminol, peroxyoxalate, lucigenin, ultraweak CL reactions, and so on. The CL mechanisms of the nanomaterial-enhanced CL systems are discussed in the first section. Nanomaterials take part in the CL reactions as the catalyst, CL emitter, energy acceptor, and reductant. Their applications are summarized in the second section. Finally, the challenges and opportunities are discussed.

Aptamer-Based Colorimetric Probe for trans-Zeatin Detection Using Unmodified Gold Nanoparticle

Trans-Zeatin is the major active phytohormone in immature corn kernels. Herein, a highly sensitive, good selective and simple aptamer-based colorimetric method for the detection of trans-zeatin was constructed. The selected aptamer sequence binds with trans-zeatin and induces a duplex-to-aptamer structure switching. The gold nanoparticles (AuNPs) solution is stable with high-concentration salt, which is protected by red complementary DNA. In the absence of trans-zeatin, the color of AuNPs changed from red to blue because aptamer DNA and complementary DNA form double-stranded DNA. Thus, the ratio of absorbance intensities (A522/A650) of AuNPs is changed with the concentration of trans-zeatin. The color change could be observed by the naked eye. The linear range of this method covers a large variation of trans-zeatin concentration from 0.05 to 0.75 μM. The detection limit is 0.037 μM. Moreover, this method was applied successfully to detect trans-zeatin in real plant samples.

Determination of hydrogen peroxide released from cancer cells by a Fe-Organic framework/horseradish peroxidase-modified electrode

Multi-walled carbon nanotubes (MWCNTs) were used as conductive carrier on the glassy carbon electrode (GCE), and the hybrid of metal organic framework [NH₂-MIL-53(Fe)] and horseradish peroxidase (HRP) was prepared by simple physical mechanical mixture. The GCE modified by the above material with immobilization, namely NH₂-MIL-53(Fe)/HRP/MWCNTs/GCE, was used to construct an electrochemical biosensor toward H₂O₂. The results indicated that the addition of NH₂-MIL-53(Fe) had a good synergistic effect on the electron transfer of HRP and the detection of H₂O₂. Under the optimized condition, the biosensor exhibited excellent electrochemical performances such as low detection limit, high sensitivity, good stability and so on. The H₂O₂ biosensor showed two linear ranges of 0.1-1 μM and 1-600 μM with a calculated detection limit of 0.028 μM (signal-to-noise ratio, S/N = 3). In addition, the stability of the hybrid of NH₂-MIL-53(Fe) and HRP were discussed by SEM, XRD and UV-vis methods. Furthermore, the reported biosensors were practically used in direct detection of H₂O₂ released from HeLa and HepG2 cells successfully. Thus, this work provides a new strategy to fabricate electrochemical biosensors using MOFs and biomolecules.

Gold nanoparticle-glutathione-functionalized porous graphene oxide-based hydrophilic beads for the selective enrichment of N-linked glycopeptides

A three-dimensional structured porous graphene oxide-polyethylenimine bead (pGP) is synthesized for immobilizing gold nanoparticles and modifying glutathione molecules (denoted as pGP/AuG). The pGP/AuG has open pore structure, honeycomb-like channels, and excellent hydrophilicity. By taking advantages of the porous structure, abundant binding sites, and multivalent interactions between glycopeptides and both glutathione molecules and free amino groups, the pGP/AuG is adopted to the selective enrichment of N-linked glycopeptides with low limit of detection (2 fmol), high enrichment selectivity (1:500), binding capacity (333.3 mg/g), recovery yield (91.3 ± 2.1%), and repeatability (< 6.0% RSD) using matrix-assisted laser desorption/ionization time of flight mass spectrometry detection method. Furthermore, the practical applicability of pGP/AuG is evaluated, in which 209 N-glycosylated peptides corresponding to 128 N-glycosylated proteins are identified from 1 μL human serum in three independent analysis procedures, suggesting the great potential for application in glycoproteome fields.Graphical abstract Schematic presentation of preparation for porous graphene oxide-based hydrophilic beads (pGP/AuG) with honeycomb-like microstructure. The pGP/AuG was successfully used for enriching and identifying glycopeptides from actual biological sample.