Microneedle-based electrochemical devices for transdermal biosensing: a review

Many research efforts over the last decade have been devoted to the development of microneedle-based diagnostic devices for minimally invasive transdermal biosensing and for long-term health monitoring. Transdermal biosensing via microneedle allows the development of minimally invasive easy-to-use point-of-care biodevices. The main objective of this short review is to provide a general overview of the most immediate and relevant progress in microneedle-based transdermal biosensing in the last five years. A critical analysis of the recent literature is finally presented.     

Photoelectrochemistry of free-base-porphyrin-functionalized zinc oxide nanoparticles and their applications in biosensing

The photoelectrochemical properties of free-base-porphyrin-functionalized zinc oxide nanoparticles were studied. A universal photoelectrochemical biosensing platform was constructed on indium tin oxide (ITO) by using the functional nanohybrid. The nanohybrid was synthesized by means of dentate binding of ZnO nanoparticles with carboxylic groups of 4,4',4',4'-(21H,23H-porphine-5,10,15,20-tetrayl)tetrakis(benzoic acid) (TCPP), and characterized with scanning electron microscopy, contact angle measurement, and spectral techniques. The nanohybrid-coated ITO electrode showed an efficient photocurrent response under irradiation at a wavelength of 360 nm, which could be greatly improved upon addition of cysteine by its oxidation at +0.3 V. The possible mechanism was that cysteine acts as a sacrificial electron donor to scavenge the photogenerated holes that locate on the excited state of TCPP, which then injects the photoexcitation electrons into the conduction band of ZnO nanoparticles, thereby transferring photoinduced electrons to the ITO electrode. Based on this enhanced photocurrent signal, a novel method for photoelectrochemical detection of cysteine was developed with a linear range of 0.6 to 157 μmol L(-1) in physiological media. The detection limit was 0.2 μmol L(-1) at a signal-to-noise ratio of 3. The novel strategy of cysteine analysis could provide an alternative method for monitoring biomolecules and extend the application of porphyrin-functionalized semiconductor nanoparticles.     

Recent advances in electrochemical sensing for hydrogen peroxide: a review

Due to the significance of hydrogen peroxide (H(2)O(2)) in biological systems and its practical applications, the development of efficient electrochemical H(2)O(2) sensors holds a special attraction for researchers. Various materials such as Prussian blue (PB), heme proteins, carbon nanotubes (CNTs) and transition metals have been applied to the construction of H(2)O(2) sensors. In this article, the electrocatalytic H(2)O(2) determinations are mainly focused on because they can provide a superior sensing performance over non-electrocatalytic ones. The synergetic effect between nanotechnology and electrochemical H(2)O(2) determination is also highlighted in various aspects. In addition, some recent progress for in vivo H(2)O(2) measurements is also presented. Finally, the future prospects for more efficient H(2)O(2) sensing are discussed.     

Enhanced electrochemical sensing of nitric oxide using a nanocomposite consisting of platinum-tungsten nanoparticles,reduced graphene oxide and an ionic liquid

We describe a high-performance nitric oxide (NO) sensor by using a nanocomposite consisting of platinum-tungsten alloy nanoparticles, sheets of reduced graphene oxide and an ionic liquid (PtW/rGO-IL) that was deposited onto the surface of a glassy carbon (GC) electrode. The modified GC electrode exhibits excellent electrocatalytic activity toward the oxidation of NO with a strong peak at 0.78 V vs. Ag/AgCl due to the synergistic effects of bimetallic PtW nanoparticles, reduced graphene oxide nanosheets and an ionic liquid. The sensor possesses a detection limit as low as 0.13 nM, high sensitivity (3.01 μA μM^?1 cm²), and good selectivity over electroactive interferents that may exist in biological systems. The sensor was tested to selectively distinguish NO in actual human serum and urine samples, confirming potential practical applications. In our perception, the approach described here may be extended to the fabrication of various kind of composites made from metal nanostructures, graphene and ionic liquids for medical and environmental analysis.

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Graphical abstract Enhanced electrochemical sensing of nitric oxide (NO) is demonstrated by utilizing the synergistic effects of bimetallic PtW nanoparticles dispersed on reduced graphene oxide and ionic liquid nanocomposite.

     

Non-enzymatic electrochemical immunoassay using noble metal nanoparticles: a review

Electrochemical immunodetection has attracted considerable attention due to its high sensitivity, low cost and simplicity. Large efforts have recently made in order to design ultrasensitive assays. Noble metal nanoparticles (NM-NPs) offer advantages such as high conductivity and large surface-to-volume ratio. NM-NPs therefore are excellent candidates for developing electrochemical platforms for immunodetection and as signal tags. The use of biofunctionalized NM-NPs often results in amplified recognition via stronger loading of signal tags, and also in enhanced signal. This review (with 87 references) gives an overview on the current state in the use of NM-NPs in Non-enzymatic electrochemical immunosensing. We discuss the application of NM-NPs as electrode matrices and as electroactive labels (either as a carrier or as electrocatalytic labels), and compare the materials (mainly nanoparticles of gold, platinum, or of bimetallic materials) in terms of performance (for example by increasing sensitivity via label amplification or via high densities of capture molecules). A conclusion covers current challenges and gives an outlook. Rather than being exhaustive, the review focuses on representative examples that illustrate novel concepts and promising applications. NM-NPs based immunosensing opens a series of concepts for basic research and offers new tools for determination of trace amounts of protein-related analytes in environment and clinical applications.

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Metal oxide nanoparticles: synthesis, characterization and application

The synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes. The main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant and the presence of adsorbing anions, the solubility of the metal oxide, and the metal oxide surface energy.     

Platinum nanoparticles functionalized nitrogen doped graphene platform for sensitive electrochemical glucose biosensing

In this work, we reported an efficient platinum nanoparticles functionalized nitrogen doped graphene (PtNPs@NG) nanocomposite for devising novel electrochemical glucose biosensor for the first time. The fabricated PtNPs@NG and biosensor were characterized using transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, static water contact angle, UV–vis spectroscopy, electrochemical impedance spectra and cyclic voltammetry, respectively. PtNPs@NG showed large surface area and excellent biocompatibility, and enhanced the direct electron transfer between enzyme molecules and electrode surface. The glucose oxidase (GOx) immobilized on PtNPs@NG nanocomposite retained its bioactivity, and exhibited a surface controlled, quasi-reversible and fast electron transfer process. The constructed glucose biosensor showed wide linear range from 0.005 to 1.1 mM with high sensitivity of 20.31 mA M⁻¹ cm⁻². The detection limit was calculated to be 0.002 mM at signal-to-noise of 3, which showed 20-fold decrease in comparison with single NG-based electrochemical biosensor for glucose. The proposed glucose biosensor also demonstrated excellent selectivity, good reproducibility, acceptable stability, and could be successfully applied in the detection of glucose in serum samples at the applied potential of −0.33 V. This research provided a promising biosensing platform for the development of excellent electrochemical biosensors.     

Nucleic acid-modulated silver nanoparticles: a new electrochemical platform for sensing chloride ion

Inorganic nanomaterials have generated considerable interest in connection to the design of biosensors. Here we exploit the DNA-induced generation of silver nanoparticles for developing an electrical biosensing protocol for chloride ions. Conjugated with thiol modified oligonucleotide, silver nanoparticles were template-synthesized and immobilized on gold electrode. During cyclic voltammogram (CV) scans, the silver nanoparticles were oxidized at high potential to form a layer of Ag/AgCl complex in the presence of Cl(-), giving off sharp solid state redox signals. Under the optimum condition, the electrode responded to Cl(-) over a dynamic range of 2.0 × 10(-5)-0.01 M, with a detection limit of 5.0 × 10(-6) M. Moreover, the specific solubility product constant-based anion recognition made the electrode applicable at a wide pH range and in complex biological systems. To demonstrate the analytical applications of this sensor in real samples, the Cl(-) concentrations in human urine were measured without any sample pretreatment. Urinary Cl(-) detected by the proposed sensor ranged from 110 to 200 mM, which was comparable to the results obtained by standard silver titration.     

Fabrication of a nanohybrid of conjugated polymer nanoparticles and graphene oxide for biosensing of trypsin

Conjugated polymers containing triphenylamine group are synthesized via Suzuki coupling polymerization. Fluorescent‐conjugated polymer nanoparticles (CPN) are prepared by reprecipitation method using the newly synthesized conjugated polymer. CPN can be encapsulated with polyarginine by electrostatic interaction. The CPN modified with polyarginine exhibit excellent interaction with graphene oxide (GO) which is chemically modified with hydrophilic groups that possesses negative charge, which, in turn, induces the quenching of the fluorescence of CPN upon formation of CPN–GO nanohybrid. Upon exposure to trypsin, the quenched fluorescence is recovered by release of CPN from the nanohybrid, because trypsin cleaves the polyarginine linkage, resulting in weakening of interaction between CPN and GO. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1898–1904     

Glycan-modified interfaces in biosensing: an electrochemical approach

Glycans (complex carbohydrates) attached to various interfacial layers represent a simple but functional model of a cellular surface, which is covered densely by glycans. In this review, we discuss interactions of surface-confined glycans with various glycan-binding proteins, viruses, or pathogenic bacteria. Such glycan receptive interfaces can be applied for biosensing of these analytes. In this review, we focus on the application of glycan interfaces for label-free electrochemical biosensing.     

Single-atom electrocatalysis: a new approach to in vivo electrochemical biosensing

Science China Chemistry - Modulation of interfacial electron transfer has been proven to pave a new approach to in vivo electrochemical monitoring of brain chemistry; however, designing and...     

Fluorescent nanoparticles for intracellular sensing: A review

Fluorescent nanoparticles (NPs), including semiconductor NPs (Quantum Dots), metal NPs, silica NPs, polymer NPs, etc., have been a major focus of research and development during the past decade. The fluorescent nanoparticles show unique chemical and optical properties, such as brighter fluorescence, higher photostability and higher biocompatibility, compared to classical fluorescent organic dyes. Moreover, the nanoparticles can also act as multivalent scaffolds for the realization of supramolecular assemblies, since their high surface to volume ratio allow distinct spatial domains to be functionalized, which can provide a versatile synthetic platform for the implementation of different sensing schemes. Their excellent properties make them one of the most useful tools that chemistry has supplied to biomedical research, enabling the intracellular monitoring of many different species for medical and biological purposes. In this review, we focus on the developments and analytical applications of fluorescent nanoparticles in chemical and biological sensing within the intracellular environment. The review also points out the great potential of fluorescent NPs for fluorescence lifetime imaging microscopy (FLIM). Finally, we also give an overview of the current methods for delivering of fluorescent NPs into cells, where critically examine the benefits and liabilities of each strategy.     

Electrochemical sensing of hydrogen peroxide using metal nanoparticles: a review

We are reviewing the state of electrochemical sensing of H₂O₂ based on the use of metal nanoparticles. The article is divided into subsections on sensors based on nanoparticles made from Ag, Pt, Pd, Cu, bimetallic nanoparticles and other metals. Some sensors display high sensitivity, fast response, and good stability. The review is subdivided into sections on sensors based on heme proteins and on nonenzymatic sensors. We also discussed the challenges of nanoscaled sensors and their future aspects.

Copper oxide nanoparticles and ionic liquid modified carbon electrode for the non-enzymatic electrochemical sensing of hydrogen peroxide

The direct electrocatalytic reduction of hydrogen peroxide in alkaline medium at a carbon ionic liquid electrode modified with copper oxide nanoparticles was investigated. The electrode was prepared by mixing graphite particles, ionic liquid (n-octylpyridium hexafluorophosphate) and copper oxide nanoparticles. Unlike the film-modified electrode, the fabrication of this electrode is simple and highly reproducible. The combination of the good conductivity of the ionic liquid and the high catalytic activity of the nanoparticles resulted in an electrode with attractive properties for the determination of hydrogen peroxide. The concentration of NaOH and the loading of copper oxide nanoparticles were optimized. The linear range for the determination of hydrogen peroxide is from 1.0 μM to 2.5 mM, the detection limit is 0.5 μM. High stability, sensitivity, selectivity and reproducibility, fast response, the ease of preparation, and surface renewal made the electrode well suitable for the determination of hydrogen peroxide in real samples.     

Peroxidase-mimicking DNAzymes for biosensing applications: a review

DNAzymes are single stranded DNA molecules that exhibit catalytic activity and are exploited in medicine, biology and material sciences. Development in this area is related to the many advantages of DNAzymes over conventional protein enzymes, such as thermal stability and simpler preparation. DNAzymes with peroxidase-like activity have recently attracted great interest. To assure such catalytic activity, oligonucleotides have to adopt a G-quadruplex structure, which can bind the hemin molecule. This system facilitates a redox reaction between the target molecule and hydrogen peroxide, which results in the appearance of an oxidized target molecule (product). DNAzymes with peroxidase-mimicking activity have great potential in bioanalytical chemistry. This review presents fundamentals concerning the design and engineering of DNAzymes with peroxidase-like activity, describes their properties and spectral characteristics and shows how DNAzymes can contribute to bioanalytical research. Examples of bioanalytical applications of DNAzymes with peroxidase-like activity include nucleic acid probes with DNAzyme labels for the detection of specific DNA sequences in colorimetric or chemiluminescent assays. Assays for telomerase or methyltransferase activity, which are potential targets in anticancer therapy, are also described in this review. Other applications include the determination of metal cations such as Ag(+), K(+), Hg(2+), Pb(2+) or Cu(2+) and amplified detection of small molecules such as adenosine, cocaine or AMP and proteins such as lysozyme or thrombin. In the last decade, DNAzymes have become part of numerous applications in many areas of science from chemistry to biology to medicine.     

Gold nanorod-based electrochemical sensing of small biomolecules: A review

Gold nanorods (AuNRs) show high potential in electrochemical sensing owing to their excellent conductivity, electrocatalytic activity, selectivity and sensitivity. This review (with 99 refs.) summarizes the performance of AuNR-based electrochemical sensors based on the use of advanced nanocomposites. Following an introduction into the fields of biosensors and nanomaterials, the article summarizes the advantages and limitations of conventional analytical methods. A third section overviews the methods for preparation and characterization of AuNRs and nanocomposites including bimetallic nanorods, gold-metal oxide, gold-carbon nanotubes, gold-polymer, gold-graphene, gold-CNT and gold-enzymes conjugates. Their electrochemistry is treated next, with aspects related to the effects of rod size and shape, of thiol coatings on voltammetric signals, and on the behavior of 1-D AuNRs and respective arrays. Section 5 gives examples for non-enzymatic sensors for simple biomolecules, with subsections on sensors for hydrogen peroxide, nitric oxide, glucose, dopamine, NAD/NADH, cysteine, and some drugs. Section 6 covers enzyme-based sensors, with examples on sensors using peroxidases, oxidases and the like. The next sections cover DNA biosensors (such as for DNA biomarkers) and immunosensors, mainly for tumor markers. Possibilities for improving sensor performance are presented at the end of the review.

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Graphical abstract Pictorial representation of gold nanorods synthesis and electrochemical sensor applications