Biosensor technology for detecting biological warfare agents: Recent progress and future trends

This review paper outlines the important issues with regards to the development of biosensors for the monitoring of biological warfare agents (BWAs) starting with the basic components of biosensors and the features of BWAs, which are compatible with detection using biological recognition molecules. The advantages and limitations of biosensors are discussed followed by the current state of the art in biosensors for detecting BWAs. Finally the developments required to enable biosensors to become more effective at providing early warning of possible biological attack and advances towards these developments are covered.     

Optical sensors and biosensors based on sol-gel films

The sol-gel technology is being increasingly used for the development of optical sensors and biosensors, due to its simplicity and versatility. By this process, porous thin films incorporating different chemical and biochemical sensing agents are easily obtained at room temperature, allowing final structures with mechanical and thermal stability as well as good optical characteristics. In this article, an overview of the state-of-the-art of sol-gel thin films-based optical sensors is presented. Applications reviewed include sensors for determination of pH, gases, ionic species and solvents, as well as biosensors.     

Recent advances in voltammetric,amperometric and ion-selective (bio)sensors fabricated by microengineering manufacturing approaches

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Three different signal amplification strategies for the impedimetric sandwich detection of thrombin

In this work, we report a comparative study on three highly specific amplification strategies for the ultrasensitive detection of thrombin with the use of aptamer sandwich protocol. The protocol consisted on the use of a first thrombin aptamer immobilized on the electrode surface, the recognition of thrombin protein, and the reaction with a second biotinylated thrombin aptamer forming the sandwich. Through the exposed biotin end, three variants have been tested to amplify the electrochemical impedance signal. The strategies included (a) silver enhancement treatment, (b) gold enhancement treatment and (c) insoluble product produced by the combination of the enzyme horseradish peroxidase (HRP) and 3-amino-9-ethylcarbazole (AEC). The properties of the sensing surface were probed by electrochemical impedance measurements in the presence of the ferrocyanide/ferricyanide redox marker. Insoluble product strategy and silver enhancement treatment resulted in the lowest detection limit (0.3 pM), while gold enhancement method resulted in the highest reproducibility, 8.8% RSD at the pM thrombin concentration levels. Results of silver and gold enhancement treatment also permitted direct inspection by scanning electron microscopy (SEM).     

Critical review of bio/nano sensors for arsenic detection

Detection of arsenic is a long-standing challenge in environmental analytical chemistry. In recent years, using biomolecules and nanomaterials for sensing arsenic has been growingly reported. In this article, this field is critically reviewed based on some recent fundamental understandings including interactions between arsenic and gold, thiol, and DNA aptamers. First, taking advantage of the adsorption of As(III) on noble metal surfaces such as silver and gold, sensors were developed based on surface enhanced Raman spectroscopy, electrochemistry and colorimetry. In addition, by functionalizing metal nanoparticles with thiol containing molecules, As(III) induced aggregation of the particles based on As(III)/thiol interactions. As(V) interacts with metal oxides strongly and competitive sensors were developed by displacing pre-adsorbed DNA oligonucleotides. A DNA aptamer was selected for As(III) and many sensors were reported based on this aptamer, although careful binding measurements indicated that the sequence has no affinity towards As(III). Overall, bio/nano systems are promising for the detection of arsenic. Future work on fundamental studies, searching for more specific arsenic binding materials and aptamers, incorporation of sensors into portable devices, and more systematic test of sensors in real samples could be interesting and useful research topics.     

Chemical and biological sensors based on organic thin-film transistors

The application of organic thin-film transistors (OTFTs) to chemical and biological sensing is reviewed. This review covers transistors that are based on the modulation of current through thin organic semiconducting films, and includes both field-effect and electrochemical transistors. The advantages of using OTFTs as sensors (including high sensitivity and selectivity) are described, and results are presented for sensing analytes in both gaseous and aqueous environments. The primary emphasis is on the major developments in the field of OTFT sensing over the last 5–10 years, but some earlier work is discussed briefly to provide a foundation.     

Challenges in the electrochemical (bio)sensing of nonelectroactive food and environmental contaminants

Electrochemical detection of nonelectroactive contaminants can be successfully faced via the use of indirect detection strategies. These strategies can provide sensitive and selective responses often coupled with portable and user-friendly analytical tools. Indirect detection strategies are usually based on the change in the signal of an electroactive probe, induced by the presence of the target molecule at a modified electrode. This critical review aims at addressing the developments in indirect electrosensing strategies for nonelectroactive contaminants in food and environmental analysis in the last few years. Emphasis is given to the strategy design, the electrode modifiers used and the feasibility of technological transfer.     

Label-Free Impedance Biosensors: Opportunities and Challenges

Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.     

Fluorescent sensors for the detection of chemical warfare agents

Along with biological and nuclear threats, chemical warfare agents are some of the most feared weapons of mass destruction. Compared to nuclear weapons they are relatively easy to access and deploy, which makes them in some aspects a greater threat to national and global security. A particularly hazardous class of chemical warfare agents are the nerve agents. Their rapid and severe effects on human health originate in their ability to block the function of acetylcholinesterase, an enzyme that is vital to the central nervous system. This article outlines recent activities regarding the development of molecular sensors that can visualize the presence of nerve agents (and related pesticides) through changes of their fluorescence properties. Three different sensing principles are discussed: enzyme-based sensors, chemically reactive sensors, and supramolecular sensors. Typical examples are presented for each class and different fluorescent sensors for the detection of chemical warfare agents are summarized and compared.     

Topical advances in nanomaterials based electrochemical sensors for resorcinol detection

The ever-increasing environmental pollution is a severe threat to the ecosystem’s healthy sustainability, and therefore environmental monitoring of these pollutants has become a burning issue throughout the world. In recent years, cost-effective, selective, portable, sensitive, and rapid sensing devices must be developed in urgent need. Advancement in nanotechnology has urged the use of different types of nanomaterials as an excellent electrode material to amplify the electrochemical detection in terms of long-term stability and electrocatalytic activity of the electrochemical sensors in addition to fulfill the aforementioned desires. This review article intimates significant advancement in developing the enzymatic and non-enzymatic electrochemical sensors based on different nanomaterials for the detection of resorcinol (RS) in the absence or presence of other phenolic compounds. This also concludes the current associated challenges as well as future perspectives for the analysis of RS in the environment. There is plethora of reported articles on RS sensors, but this review mainly discusses the selective reports on the applications of RS sensors.     

“Clickable” affinity ligands for effective separation of glycoproteins

In this paper, we present a new modular approach to immobilize boronic acid ligands that can offer effective separation of glycoproteins. A new “clickable” boronic acid ligand was synthesized by introducing a terminal acetylene group into commercially available 3-aminophenyl boronic acid. The clickable ligand, 3-(prop-2-ynyloxycarbonylamino)phenylboronic acid (2) could be easily coupled to azide-functionalized hydrophilic Sepharose using Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction under mild condition. Compared to other boronic acid affinity gels, the new affinity gel displayed superior effectiveness in separating model glycoproteins (ovalbumin and RNase B) from closely related bovine serum albumin and RNase A in the presence of crude Escherichia coli proteins. Because of the simplicity of the immobilization through “click chemistry”, the new ligand 2 is expected to not only offer improved glycoprotein separation in other formats, but also act as a useful building block to develop new chemical sensors for analysis of other glycan compounds.     

Gas sensors based on metal-organic frameworks:Challenges and opportunities

The need for high-performance and cost-effective gas sensors in industrial and domestic settings has led to ad-vancements in gas sensors based on metal-organic frameworks(MOFs).However,challenges remain in the design and synthesis of MOFs with customized structure and affinity toward targeted gases and their integration onto miniaturized electronic devices.The deliberate design of MOFs with desired characteristics is hindered by limited understanding of the interactions between MOFs and analytes.Furthermore,there is a lack of customization of relevant MOF-based sensors with salient sensing performance and their integration into sensor arrays to align with different application scenarios.The combination of machine learning or artificial intelligence(AI)with gas sensors also represents a promising avenue for future research.Herein,we provide a mini-review of recent ac-complishments in MOF-based gas sensors,covering materials design and device integration.The challenges of miniaturization and building smart sensing systems with anomaly detection,self-calibration,and lifetime pre-diction are also discussed.     

Electrochemical Biosensors for Cancer Biomarkers Detection: Recent Advances and Challenges

Biomarkers are described as characteristics that provide information about biological conditions whether normal or pathological. Detection of biomarkers at the earliest stage of the cancer is of utmost importance for clinical diagnosis. Electrochemical biosensors allow detecting the low levels of specific analytes in blood, urine or saliva and providing a sensitive approach for direct measurement for cancer biomarker detection. Moreover, the integration of electrochemical devices with nanomaterials, such as carbon nanotubes, gold and magnetic particles offer amplification and multiplexing capabilities for simultaneous measurements of cancer biomarkers very sensitively. This review summarizes the recent developments of electrochemical biosensors systems for the detection of cancer biomarkers with emphasis on voltammetric, amperometric and impedimetric biosensors. A special attention is paid to aptamers and miRNAs that are very promising for the ultra‐sensitive and specific cancer biomarker detection.     

Electrochemical sensors for environmental gas analysis

The application of electrochemical sensors for measurement of concentration of pollutant gases in air in the part-per-billion (10⁹) range is reviewed. Performance-limiting factors, particularly the effects of extremes and of relatively rapid changes in ambient temperature and humidity, are noted. Variations in composition of the electrolyte in the meniscus at the electrode–gas interface and instability of the solid–liquid–gas contact line, causing important variations in current due to background electrode reactions, are deduced and suggested as the reason for the performance limitations. Suggestions are made for mitigation through instrument design.     

Enzymatic detection of glucose using fluoride-selective electrodes with polymeric membranes

The feasibility of using polymeric membrane fluoride-selective electrodes based on zirconium(IV) 5,10,15,20-tetraphenylporphyrin as a detector in a flow-injection analysis (FIA) system for glucose determination was examined. The optimization of enzymatic reactions, FIA system configuration and enzyme-immobilization process was performed. It was shown that the resulting flow-injection system exhibits good working parameters, such as reproducibility, linear range of glucose concentration (3 × 10⁻³–10⁻¹ M), sampling rate (60 samples per minute) and lifetime (over 1 month). The performance of the polymeric membrane electrode was similar to that of a crystalline LaF₃ electrode. The results of glucose determination in synthetic samples with the proposed system show good agreement with real glucose concentrations.     

Optical sensors for determination of heavy metal ions

A review is given on optical means for single shot testing (probing) as well as continuous monitoring (sensing) of heavy metal ions (HMs). Following an introduction into indicator based approaches, we discuss the types of indicator dyes and polymeric supports used, as well as existing sensing schemes for HMs. The wealth of information is compiled in the form of tables and critically reviewed. Notwithstanding the tremendous work performed so far, it is obvious that still severe limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. On the other hand, such sensors have found — and will find — their application whenever rapid and cost-effective testing is required, where personnel is scarce or unskilled, and in field tests. Despite their limitations, the number of such sensors (and of irreversible probes) for HMs is likely to increase in future.     

Pepsin‐modified chiral monolithic column for affinity capillary electrochromatography

Pepsin‐modified affinity monolithic capillary electrochromatography, a novel microanalysis system, was developed by the covalent bonding of pepsin on silica monolith. The column was successfully applied in the chiral separation of (±)‐nefopam. Furthermore, the electrochromatographic performance of the pepsin‐functionalized monolith for enantiomeric analysis was evaluated in terms of protein content, pH of running buffer, sample volume, buffer concentration, applied voltage, and capillary temperature. The relative standard deviation (%RSD) values of retention time (intraday <0.53, n = 10; interday <0.53, n = 10; column‐to‐column <0.70, n = 20; and batch‐to‐batch <0.80, n = 20) indicated satisfactory stability of these columns. No appreciable change was observed in retention and resolution for chiral recognition of (±)‐nefopam in 50 days with 100 injections. The proteolytic activity of this stationary phase was further characterized with bovine serum albumin as substrate for online protein digestion. As for monolithic immobilized enzyme reactor, successive protein injections confirmed both the operational stability and ability to reuse the bioreactor for at least 20 digestions. It implied that the affinity monolith used in this research opens a new path of exploring particularly versatile class of enzymes to develop enzyme‐modified affinity capillary monolith for enantioseparation.     

One-step fabrication of glucose sensors based on entrapment of glucose oxidase within poly(ester-sulfonic acid) coatings

A simple, rapid, reproducible and effective one-step procedure for biosensor construction, based on casting mixed poly(ester-sulfonic acid)-glucose oxidase solutions onto solid electrodes is described. The cation exchanger simultaneously performs the entrapment, charge permselectivity and antifouling functions. The discrimination against potential interferences is accompanied with a fast and sensitive response to glucose. With flow injection operation, 180 samples can be processed per hour, with a detection limit of 3 × 10^?6 M. The effects of numerous experimental variables are explored. These properties of poly(ester-sulfonic acid) ionomers, coupled with their availability as aqueous dispersions, make them attractive and versatile for biosensor work.