Current aspects in immunosensors

Paper-based biosensors relying on core biological immune scaffolds for the detection of procymidone in vegetables

In order to achieve a highly sensitive detection of procymidone in vegetables, three paper-based biosensors based on a core biological immune scaffold (CBIS) were developed, which were time-resolved fluorescence immunochromatography strips with Europium (III) oxide (Eu-TRFICS). Goat anti-mouse IgG and europium oxide time-resolved fluorescent microspheres formed secondary fluorescent probes. CBIS was formed by secondary fluorescent probes and procymidone monoclonal antibody (PCM-Ab). The first type of Eu-TRFICS (Eu-TRFICS-(1)) fixed secondary fluorescent probes on a conjugate pad, and PCM-Ab was mixed with a sample solution. The second type of Eu-TRFICS (Eu-TRFICS-(2)) fixed CBIS on the conjugate pad. The third type of Eu-TRFICS (Eu-TRFICS-(3)) was directly mixed CBIS with the sample solution. They solved the problems of steric hindrance of antibody labeling, insufficient exposure of antigen recognition region and easy loss of activity in traditional methods. They realized multi-dimensional labeling and directional coupling. They replaced the loss of antibody activity. And the three types of Eu-TRFICS were compared, among which Eu-TRFICS-(1) was the best detection choice. Antibody usage was reduced by 25% and sensitivity was increased by 3 times. Its detection range was 1-800 ng/mL, the limit of detection (LOD) was 0.12 ng/mL with the visible LOD (vLOD) of 5 ng/mL.

Advances in immunoassay-based strategies for mycotoxin detection in food: From single-mode immunosensors to dual-mode immunosensors

Mycotoxin contamination in foods and other goods has become a broad issue owing to serious toxicity, tremendous threat to public safety, and terrible loss of resources. Herein, it is necessary to develop simple, sensitive, inexpensive, and rapid platforms for the detection of mycotoxins. Currently, the limitation of instrumental and chemical methods cannot be massively applied in practice. Immunoassays are considered one of the best candidates for toxin detection due to their simplicity, rapidness, and cost-effectiveness. Especially, the field of dual-mode immunosensors and corresponding assays is rapidly developing as an advanced and intersected technology. So, this review summarized the types and detection principles of single-mode immunosensors including optical and electrical immunosensors in recent years, then focused on developing dual-mode immunosensors including integrated immunosensors and combined immunosensors to detect mycotoxins, as well as the combination of dual-mode immunosensors with a portable device for point-of-care test. The remaining challenges were discussed with the aim of stimulating future development of dual-mode immunosensors to accelerate the transformation of scientific laboratory technologies into easy-to-operate and rapid detection platforms.

Molecular imprinting-based sensors: Lab-on-chip integration and biomedical applications

The innovative technology of a marketable lab-on-a-chip platform for point-of-care (POC) in vitro detection has recently attracted remarkable attention. The POC tests can significantly enhance the high standard of medicinal care. In the last decade, clinical diagnostic technology has been broadly advanced and successfully performed in several areas. It seems that lab-on-a-chip approaches play a significant role in these technologies. However, high-cost and time-consuming methods are increasing the challenge and the development of a cost-effective, rapid and efficient method for the detection of biomolecules is urgently needed. Recently, polymer-coated sensing platforms have been a promising area that can be employed in medical diagnosis, pharmaceutical bioassays, and environmental monitoring. The designed on-chip sensors are based on molecular imprinting polymers (MIPs) that use label-free detection technology. Molecular imprinting shines out as a potentially promising technique for creating artificial recognition material with molecular recognition sites. MIPs provide unique advantages such as excellent recognition specificity, high selectivity, and good reusability. This review article aims to define several methods using molecular imprinting for biomolecules and their incorporation with several lab-on-chip technologies to describe the most promising methods for the development of sensing systems based on molecularly imprinted polymers. The higher selectivity, more user-friendly operation is believed to provide MIP-based lab-on-a-chip devices with great potential academic and commercial value in on-site clinical diagnostics and other point-of-care assays.

Carbon-Based Fluorescent Nano-Biosensors for the Detection of Cell-Free Circulating MicroRNAs

Currently, non-communicable diseases (NCDs) have emerged as potential risks for humans due to adopting a sedentary lifestyle and inaccurate diagnoses. The early detection of NCDs using point-of-care technologies significantly decreases the burden and will be poised to transform clinical intervention and healthcare provision. An imbalance in the levels of circulating cell-free microRNAs (ccf-miRNA) has manifested in NCDs, which are passively released into the bloodstream or actively produced from cells, improving the efficacy of disease screening and providing enormous sensing potential. The effective sensing of ccf-miRNA continues to be a significant technical challenge, even though sophisticated equipment is needed to analyze readouts and expression patterns. Nanomaterials have come to light as a potential solution as they provide significant advantages over other widely used diagnostic techniques to measure miRNAs. Particularly, CNDs-based fluorescence nano-biosensors are of great interest. Owing to the excellent fluorescence characteristics of CNDs, developing such sensors for ccf-microRNAs has been much more accessible. Here, we have critically examined recent advancements in fluorescence-based CNDs biosensors, including tools and techniques used for manufacturing these biosensors. Green synthesis methods for scaling up high-quality, fluorescent CNDs from a natural source are discussed. The various surface modifications that help attach biomolecules to CNDs utilizing covalent conjugation techniques for multiple applications, including self-assembly, sensing, and imaging, are analyzed. The current review will be of particular interest to researchers interested in fluorescence-based biosensors, materials chemistry, nanomedicine, and related fields, as we focus on CNDs-based nano-biosensors for ccf-miRNAs detection applications in the medical field.

Recent Advances in Rapid Detection Techniques for Pesticide Residue: A Review

As an important chemical pollutant affecting the safety of agricultural products, the on-site and efficient detection of pesticide residues has become a global trend and hotspot in research. These methodologies were developed for simplicity, high sensitivity, and multiresidue detection. This review introduces the currently available technologies based on electrochemistry, optical analysis, biotechnology, and some innovative and novel technologies for the rapid detection of pesticide residues, focusing on the characteristics, research status, and application of the most innovative and novel technologies in the past 10 years, and analyzes challenges and future development prospects. The current review could be a good reference for researchers to choose the appropriate research direction in pesticide residue detection.

Study on a Natural Silk Cocoon Membrane-Based Versatile and Stable Immunosensing Platform via Directional Immunoaffinity Recognition

The development of immunosensing assays for in vitro diagnostics has attracted great attention in recent years. Various substrate materials and immobilization methods of biomolecules were exploited for immunosensors, but their bioactivity and longevity have been facing serious challenges. To address this limitation, we investigated a natural silk cocoon membrane as immunosensing substrate material. By using its intrinsic properties, the target biomolecules were immobilized on the membrane through directional immunoaffinity recognition. The silk cocoon membrane-based immunosensor showed great potential for both qualitative and quantitative immunoassays, through naked-eye observation or analyzing the change in red color intensity, respectively. The immunosensor exhibited significant detection capability for anti-D (titer 1:1024) sensitized red blood cells. The colorimetric responses of concentrations ranged from 1 μg/mL to 1 ng/mL, and the detection limit for anti-D was 3.4 ng/mL. The immunosensor also showed excellent stability for the immobilized antibodies when stored at 4 and 25 °C; the bioactivity remained unchanged or slightly declined within 40 weeks. Even at 37 °C, the bioactivity began to decline after 12 weeks. This current work highlights the potential of using the natural silk cocoon membrane as a substrate for a versatile and thermally stable immunosensing platform for application in immunoassays.

Comparison of Physical Adsorption and Covalent Coupling Methods for Surface Density-Dependent Orientation of Antibody on Silicon

The orientation of antibodies, employed as capture molecules on biosensors, determines biorecognition efficiency and bioassay performance. In a previous publication we demonstrated for antibodies attached covalently to silicon that an increase in their surface amount Γ, evaluated with ellipsometry, induces changes in their orientation, which is traced directly using Time-of-Flight Secondary Ion Mass Spectroscopy combined with Principal Component Analysis. Here, we extend the above studies to antibodies adsorbed physically on a 3-aminopropyltriethoxysilane (APTES) monolayer. Antibodies physisorbed on APTES (0 ≤ Γ ≤ 3.5 mg/m²) reveal the Γ ranges for flat-on, side-on, and vertical orientation consistent with random molecular packing. The relation between orientation and Γ is juxtaposed for silicon functionalized with APTES, APTES modified with glutaraldehyde (APTES/GA) and N-hydroxysuccinimide-silane (NHS-silane). Antibody reorientation occurs at lower Γ values when physisorption (APTES) is involved rather than chemisorption (APTES/GA, NHS-silane). At high Γ values, comparable proportions of molecules adapting head-on and tail-on vertical alignment are concluded for APTES and the NHS-silane monolayer, and they are related to intermolecular dipole–dipole interactions. Intermolecular forces seem to be less decisive than covalent binding for antibodies on the APTES/GA surface, with dominant head-on orientation. Independently, the impact of glutaraldehyde activation of APTES on vertical orientation is confirmed by separate TOF-SIMS measurements.

Developing a Biosensor-Based Immunoassay to Detect HPV E6 Oncoprotein in the Saliva Rinse Fluid of Oral Cancer Patients

Transmission of Human papillomavirus (HPVs) is faithfully associated with carcinogenesis of oral cavity and oropharyngeal cancers. Therefore, clinical researchers may need to generate customized antibodies for the upcoming ELISA-based analysis to discover rare but valuable biomarkers. The aim of study was to develop and generate a biosensor-based immunoassay for early screening HPV-related oral cancer via saliva rinse fluid analysis. A peptide fragment of high-risk HPV subtype 16/18 protein, E6 protein (HP-1 protein sequence 48–66), was designed and synthesized, followed by the generation of polyclonal antibodies (anti-HP1 IgY) in our university-based laboratories. The titer and specificity of antibodies were determined by enzyme-linked immunosorbent assay (ELISA), and the Surface Plasmon Resonance (SPR) biosensor-based method was developed. Kinetic analyses by SPR confirmed that this designed peptide showed a high affinity with its generated polyclonal antibodies. Saliva fluid samples of thirty oral cancer patients and 13 healthy subjects were analyzed. SPR indicated that 26.8% of oral cancer patients had higher resonance unit (ΔRU) values than normal subjects. In conclusion, we developed a biosensor-based immunoassay to detect HPV E6 oncoprotein in the saliva rinse fluid for early screening and discrimination of HPV-related oral cancer patients.

In silico antibody engineering for SARS-CoV-2 detection

Engineered immunoglobulin-G molecules (IgGs) are of wide interest for the development of detection elements in protein-based biosensors with clinical applications. The strategy usually employed for the de novo design of such engineered IgGs consists on merging fragments of the three-dimensional structure of a native IgG, which is immobilized on the biosensor surface, and of an antibody with an exquisite target specificity and affinity. In this work conventional and accelerated classical molecular dynamics (cMD and aMD, respectively) simulations have been used to propose two IgG-like antibodies for COVID-19 detection. More specifically, the crystal structure of the IgG1 B12 antibody, which inactivates the human immunodeficiency virus-1, has been merged with the structure of the antibody CR3022 Fab tightly bounded to SARS-CoV-2 receptor-binding domain (RBD) and the structure of the S309 antibody Fab fragment complexed with SARS-CoV-2 RBD. The two constructed antibodies, named IgG1-CR3022 and IgG1-S309, respectively, have been immobilized on a stable gold surface through a linker. Analyses of the influence of both the merging strategy and the substrate on the stability of the two constructs indicate that the IgG1-S309 antibody better preserves the neutralizing structure than the IgG1-CR3022 one. Overall, results indicate that the IgG1-S309 is appropriated for the generation of antibody based sensors for COVID-19 diagnosis.

Biomolecular assembly on interdigitated electrode nanosensor for selective detection of insulin-like growth factor-1

This research is focussed to quantify IGF1 by electroanalytical analysis on InterDigitated electrode surface and characterized by the microscopic observations. For the detection, antibody and aptamer were used to analyze the level of IGF1. The sandwich pattern (aptamer-IGF1-antibody) was designed on the chemically modified IDE surface and reached the limit of detection to 10 fM with 100 folds enhancement in the sensitivity. Different control experiments (absence of IGF1, binding with IGF2 and with non-complementary aptamer) were failed to show the current changes, discriminated the specific detection. A good detection strategy is to complement the currently following imaging systems for AAA.

Advances in diagnosis of Helicobacter pylori through biosensors: Point of care devices

Invasive as well as non-invasive conventional techniques for the detection of Helicobacter pylori (H. pylori) have several limitations that are being overcome by the development of novel, rapid and reliable biosensors. Herein, we describe several biosensors fabricated for the detection of H. pylori. This review aims to provide the principles of biosensors and their components including in the context to H. pylori detection. The major biorecognition elements in H. pylori detection include antigen/antibodies, oligonucleotides and enzymes. Furthermore, the review describes the transducers, such as electrochemical, optical and piezoelectric, also including microfluidics approaches. An overview of the biomarkers associated with H. pylori pathogenesis is also discussed. Finally, the prospects of advancement and commercialization of point-of-care tools are summarized.

A sequentially bioconjugated optofluidic laser for wash-out-free and rapid biomolecular detection

Microstructures can improve both sensitivity and assay time in heterogeneous assays (such as ELISA) for biochemical analysis; however, it remains a challenge to perform the essential wash process in those microstructure-based heterogeneous assays. Here, we propose a sequential bioconjugation protocol to solve this problem and demonstrate a new type of fiber optofluidic laser for biosensing. Except for acting as an optical microresonator and a microstructured substrate, the miniaturized hollow optical fiber (HOF) is used as a microfluidic channel for storing and transferring reagents thanks to its capability in length extension. Through the capillary action, different reagents were sequentially withdrawn into the fiber for specific binding and washing purposes. By using the sequentially bioconjugated FOFL, avidin molecules are detected based on competitive binding with a limit of detection of 9.5 pM, ranging from 10 pM to 100 nM. It is demonstrated that a short incubation time of 10 min is good enough to allow the biomolecules to conjugate on the inner surface of the HOF. Owing to its miniaturized size, only 589 nL of liquid is required for incubation, which reduces the sample consumption and cost for each test. This work provides a tool to exploit the potential of microstructured optical fibers in high-performance biosensing.

Protein-nanoparticle interactions and a new insight

The study of protein-nanoparticle interactions provides knowledge about the bio-reactivity of nanoparticles, and creates a database of nanoparticles for applications in nanomedicine, nanodiagnosis, and nanotherapy. The problem arises when nanoparticles come in contact with physiological fluids such as plasma or serum, wherein they interact with the proteins (or other biomolecules). This interaction leads to the coating of proteins on the nanoparticle surface, mostly due to the electrostatic interaction, called 'corona'. These proteins are usually partially unfolded. The protein corona can deter nanoparticles from their targeted functionalities, such as drug/DNA delivery at the site and fluorescence tagging of diseased tissues. The protein corona also has many repercussions on cellular intake, inflammation, accumulation, degradation, and clearance of the nanoparticles from the body depending on the exposed part of the proteins. Hence, the protein-nanoparticle interaction and the configuration of the bound-proteins on the nanosurface need thorough investigation and understanding. Several techniques such as DLS and zeta potential measurement, UV-vis spectroscopy, fluorescence spectroscopy, circular dichroism, FTIR, and DSC provide valuable information in the protein-nanoparticle interaction study. Besides, theoretical simulations also provide additional understanding. Despite a lot of research publications, the fundamental question remained unresolved. Can we aim for the application of functional nanoparticles in medicine? A new insight, given by us, in this article assumes a reasonable solution to this crucial question.

Aluminum Microcomb Electrodes on Silicon Wafer for Detecting Val66Met Polymorphism in Brain-Derived Neurotrophic Factor

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) dysregulation is widely related with various psychiatric and neurological disorders, including schizophrenia, depression, Rett syndrome, and addiction, and the available evidence suggests that BDNF is also highly correlated with Parkinson's and Alzheimer's diseases.

METHODS

The BDNF target sequence was detected on a capture probe attached on aluminum microcomb electrodes on the silicon wafer surface. A capture-target-reporter sandwich-type assay was performed to enhance the detection of the BDNF target.

RESULTS

The limit of detection was noticed to be 100 aM. Input of a reporter sequence at concentrations >10 aM improved the detection of the target sequence by enhancing changes in the generated currents. Control experiments with noncomplementary and single- and triple-mismatches of target and reporter sequences did not elicit changes in current levels, indicating the selective detection of the BDNF gene sequence.

CONCLUSION

The above detection strategy will be useful for the detection and quantification of BDNF, thereby aiding in the provision of suitable treatments for BDNF-related disorders.

Thyroglobulin determination on silane-antibody functionalized interdigitated dielectrode surface to diagnose thyroid tumor

Thyroid cancer appears in endocrine glands and specific to thyroid glands has been reported widely. This work was targeted to identify and quantify thyroglobulin by using antithyroglobulin antibody complexed silane surface on interdigitated electrode (IDE) sensing surface. (3-Aminopropyl)triethoxysilane linker was used to make silane-coupling with antibody and attached on the hydroxylated IDE. This electroanalytical IDE revealed the dose-dependent responses with thyroglobulin concentrations. By getting increments with the thyroglobulin concentrations, the current responses were enhanced concomitantly and the thyroglobulin detection limit was noted as 1 pM on the linear curve [y = 0.1311x + 0.5386; R² = 0.9707] with the sensitivity at lower picomolar range. Moreover, the control experiments with thyroid peroxidase and nonimmune antibody cannot yield any response of current, confirming the specific detection of thyroglobulin. This research set-up is useful to determine and quantify the thyroglobulin and diagnose thyroid cancer.

Antibody immobilization techniques in mass sensitive immunosensor: enhanced sensitivity through limited mass load

Background:

Biosensors are analytical devices that include a sample-delivery approach between a biological recognition element and a transducer required to convert the physicochemical change produced from the interaction of biological molecules-receptor interaction into signal. The immunosensor is a special type of biosensors that includes an antibody as a biorecognition element to detect analyte as antigens. In mass-sensitive sensors, antigen-antibody interactions can be specified by measuring the frequency change and most commonly knowns are surface acoustic wave, bulk acoustic wave, quartz crystal microbalance and microcantilevers.

Methods:

Different methods for antibody immobilization including functionalization of the transducer surface with specific groups have been reported for antibody immobilization. This stage affects the limit of detection and overall performance. In this review, perspectives on immobilization strategies of mass sensitive immunosensors according to transducer types will be presented. The choice of immobilization methods and their impact on performance in terms of capture molecule loading, orientation and signal improvement is will also be discussed.

Results:

One of the most critical point during configuration of the biorecognition layer is to improve the sensitivity. Therefore, we initially focused on comparisons of the antibody immobilization strategies in the biorecognition layer in terms of mass load level and high sensitivity.

Conclusion:

The lack of significant data on the mass accumulations up to the functionalization and antibody immobilization steps, which are the basis of immusensor production, has been identified. However, mass sensitive immunosensors have the potential to become more common and effective analytical devices for many application areas.

Broad-spectrum electrochemical immunosensor based on one-step electrodeposition of AuNP-Abs and Prussian blue nanocomposite for organophosphorus pesticide detection

Broad-spectrum antibodies can effectively recognize substances with similar structures and have broad application prospects in field rapid detection. In this study, broad-spectrum antibodies (Abs) against organophosphorus pesticides (OPs) were used as sensitive recognition elements, which could effectively recognize most OPs. Gold nanoparticles (AuNPs) have good biocompatibility. It combined with Abs to form a gold-labeled probe (AuNPs-Abs), which enhances the effective binding of antibodies to nanomaterials. Prussian blue (PB) was added to electrodeposition solution to enhance the conductivity, resulting in superior electrochemical performance. The AuNP-Abs-PB composite film was prepared by electrodeposition on the electrode surface to improve the anti-interference ability and stability of the immunosensor. Under the optimal experimental conditions, the immunosensor had a wide detection range (IC₂₀-IC₈₀: 1.82 × 10^-3-3.29 × 10⁴ ng/mL) and high sensitivity. Most importantly, it was simple to be prepared and could be used to detect multiple OPs.

Toward a nanopaper-based and solid phase immunoassay using FRET for the rapid detection of bacteria

In this study, we propose a novel sensitive solid-based immunosensor developed on a plasmonic nanopaper platform for the detection of Escherichia coli (E. coli) bacteria. This plasmonic nanopaper that comprises of carboxylated bacterial cellulose (CBC) impregnated with gold nanoparticles (AuNP-CBC), employed as a quencher and a sustainable functionalized platform to be conjugated with protein A. Thus, the conjugated protein A allows the aligned linkage of EAb-QD (anti-E. coli conjugated quantum dot) and EAb-AF (anti-E. coli conjugated Alexa Fluor 488). Interestingly, once E. coli was captured by the AuNP-CBC/EAb-QD or AuNP-CBC/EAb-AF, the energy transfer from the QD or Alexa Fluor fluorophores is triggered due to the conformational change in the antibody structure and this, in turn, causes a decrease in the distance between fluorophores and the quencher nanopaper and, therefore diminishing their photoluminescence. The immunosensors performed successfully to recognize E. coli at concentrations as low as 50 CFU mL⁻¹ in the standard buffer. The examined functionality of the immunosensors in a real matrix such as chicken extract and lettuce juice demonstrated a highly efficient response while QD is the main fluorophore with a limit of detection around 100 CFU mL⁻¹.

Controlling orientation, conformation, and biorecognition of proteins on silane monolayers, conjugate polymers, and thermo-responsive polymer brushes: investigations using TOF-SIMS and principal component analysis

Control over orientation and conformation of surface-immobilized proteins, determining their biological activity, plays a critical role in biointerface engineering. Specific protein state can be achieved with adjusted surface preparation and immobilization conditions through different types of protein-surface and protein-protein interactions, as outlined in this work. Time-of-flight secondary ion mass spectroscopy, combining surface sensitivity with excellent chemical specificity enhanced by multivariate data analysis, is the most suited surface analysis method to provide information about protein state. This work highlights recent applications of the multivariate principal component analysis of TOF-SIMS spectra to trace orientation and conformation changes of various proteins (antibody, bovine serum albumin, and streptavidin) immobilized by adsorption, specific binding, and covalent attachment on different surfaces, including self-assembled monolayers on silicon, solution-deposited polythiophenes, and thermo-responsive polymer brushes. Multivariate TOF-SIMS results correlate well with AFM data and binding assays for antibody-antigen and streptavidin-biotin recognition. Additionally, several novel extensions of the multivariate TOF-SIMS method are discussed.

Graphical abstract

Immunodetection of urinary C-terminal telopeptide fragment of type II collagen: An osteoarthritis biomarker analysis

The urinary C-terminal telopeptide fragment of type II collagen (uCTX-II) has been reported as the efficient blood-based biomarker for osteoarthritis, which affects knees, hands, spine, and hips. This study reports a sensing strategy with antibody-conjugated gold nanoparticles (GNP) on an interdigitated electrode (IDE) to determine uCTX-II. The GNP-antibody complex was chemically immobilized on the IDE surface through the amine linker. uCTX-II was determined by monitoring the alteration in current upon interacting the GNP-complexed antibody. This strategy was improved the detection by attracting higher uCTX-II molecules, and the detection limit falls in the range of 10-100 pM with an acceptable regression value [y = 0.6254x - 0.4073, R² = 0.9787]. The sensitivity of the detection was recognized at 10 pM. Additionally, upon increasing the uCTX-II concentration, the current changes were increased in a linear fashion. Control detection with nonimmune antibody and control protein do not increase the current level, confirming the specific detection of uCTX-II. This method of detection helps in diagnosing osteoarthritis and its follow-up treatment.

The application of antibody-aptamer hybrid biosensors in clinical diagnostics and environmental analysis

The growing number of various diseases and the increase of environmental contamination are the causes for the development of novel methods for their detection. The possibility of the application of affinity-based biosensors for such purposes seems particularly promising as they provide high selectivity and low detection limits. Recently, the usage of hybrid antibody-aptamer sandwich constructs was shown to be more advantageous in terms of working parameters in comparison to aptamer-based and immune-based biosensors. This review is focused on the usage of hybrid antibody-aptamer receptor layers for the determination of clinically and environmentally important target molecules. In this work, antibodies and aptamer molecules are characterized and the methods of their immobilization as well as analytical signal generation are shown. This is followed by the critical presentation of examples of hybrid sandwich biosensors that have been elaborated in the past 12 years.

An ultrasensitive Cystatin C renal failure immunosensor based on a PPy/CNT electrochemical capacitor grafted on interdigitated electrode

An interdigitated immunosensor for Cystatin C detection based on polypyrrole/carbon nanotube electrochemical capacitor is described. Cystatin C (CysC) is powerful biomarker for early acute renal failure and one predictive for cardiovascular risk, sepsis, cancer and death. Recently, electrochemical immunosensors based on interdigitated electrodes (IDE) have been successfully focused on development of point-of-care testing, due to their miniaturization facilities and higher sensitivity as compared with the screen-printed electrochemical sensing. Herein, a polypyrrole/carbon nanotube nanoyhibrid film was grafted on two gold fingers by electropolymerization obtaining a supercapacitor. Anti-CysC antibodies were immobilized on the IDE by covalent entrapment via ethylenediamine bifunctional agent, followed by glycine blocking in acid and alkaline medium. Under low frequency, capacitive effect of antigen-antibody interaction were observed by double layer capacitance, and analytical responses of this IDE immunosensor to CysC serum were obtained by changes on phase angle a linear range up to 300 ng/mL. The cutoff was calculated for serum samples showing a total reducing of non-specific binding at approximately 28 ng/mL CysC. This immunosensor based on interdigitated electrode (IDE) is a potential tools as portable device,with possibility to use as a practical and rapid test for CysC diagnostic in samples of serum.

Preparation and characterization of carboxymethyl cashew gum grafted with immobilized antibody for potential biosensor application

This report details the design of carboxymethylated cashew gum (CG) as a platform for antibody (Ab) immobilization, which can then be used as a biosensor for bacteria detection. The CG was isolated and characterized, followed by conversion to carboxymethyl cashew gum (CMCG). The CMCG film was a viable support for antibody immobilization; it was electrodeposited on gold surface using the cyclic voltammetry technique, applying a potential sweep from -1.0 V to 1.3 V with a scan rate of 50 mV s^-1 and 10 scans. The COOH groups on the surface of the film were critical in promoting Ab bonding. The immobilization of the Ab was mediated by protein A (PrA) for recognition of the antigen. Voltammetry studies were used to monitor the antibody immobilization. Finally, the analytical response of the CMCG-PrA-Ab system was evaluated with the chronoamperometry technique and was found to detect Salmonella Typhimurium bacteria rapidly and efficiently.

High-performance detection of an abdominal aortic aneurysm biomarker by immunosensing

Abdominal aortic aneurysm (AAA) is a serious, life-threatening vascular disease that presents as an enlarged area of the aorta, which is the main artery that carries blood away from the heart. AAA may occur at any location in the aorta, but it is mainly found in the abdominal region. A ruptured AAA causes serious health issues, including death. Traditional imaging techniques, such as computed tomography angiogram, magnetic resonance imaging, and ultrasound sonography, have been used to identify AAAs. Circulating biomarkers have recently become attractive for diagnosing AAAs due to their cost-effectiveness compared to imaging. Insulin-like growth factor 1 (IGF-1), a secreted hormone vital for human atherosclerotic plaque stability, has been found to be an efficient biomarker for AAA identification. In this report, immunosensing was performed by using an InterDigitated electrode (IDE) sensor to detect circulating levels of IGF-1. The detection limit of IGF-1 was found to be 100 fM with this sensor. Moreover, related protein controls (IGF-2 and IGFBP3) were not detected with the same antibody, indicating selective IGF-1 detection. Thus, immunosensing by using an IDE sensor may help to effectively diagnose AAAs and represents a basic platform for further development.

Biosensors on the road to early diagnostic and surveillance of Alzheimer's disease

Alzheimer's disease is a debilitating and largely untreatable condition with subtle onset and slow progression over an extensive period of time, which culminate in increasing levels of disability. As Alzheimer's disease prevalence is expected to grow exponentially in the upcoming decades, there is an urgency to develop analytical technologies for the sensitive, reliable and cost-effective detection of Alzheimer's disease biomarkers. Biosensors are powerful analytical devices that translate events of biological recognition on physical or chemical transducers into electrical, thermal or optical signals. The high sensitivity and selectivity of biosensors associated with easy, rapid and low-cost determination of analytes have made this discipline one of the most intensively studied in the past decades. This review centers on recent advances, challenges and trends of Alzheimer's disease biosensing particularly in the effort to combine the unique properties of nanomaterials with biorecognition elements. In the last decade, impressive progresses have been made towards the development of biosensors, mainly electrochemical and optical, for detection of Alzheimer's disease biomarkers in the pico- and femto-molar range. Nonetheless, advances in multiplexed detection, robustness, stability and specificity are still necessary to ensure an accurate and differentiated diagnosis of this disease.

Disposable electrochemical immunosensor for analysis of cystatin C, a CKD biomarker

Specific monitoring of cystatin C (CysC) levels in biological fluids is critical for diagnosis, treatment and mechanistic understanding of a spectrum of diseases, particularly chronic kidney disease (CKD). Despite evidences that CysC correlates with the high risk and/or progression of CKD, its use in clinical practice is still scarce. In this context, we report the development of a simple and sensitive immunosensor for the detection of CysC. The biosensor combines the technology of cost-effective screen-printed electrodes with the high specificity of a sandwich immunoassay. Optimized conditions showed that the sensor operates in a linear range between 10 and 100 ng mL^-1, with a detection limit and a sensitivity of 6.0 ng mL^-1 and 6.4 ± 0.3 μA ng mL^-1 cm^-2, respectively. Moreover, the sensor provided precise results (RSD ≤ 6.2%) and the quantification of CysC in CKD serum samples revealed to be in agreement with the values obtained by a particle-enhanced nephelometric immunoassay. In this light, the proposed immunosensor qualifies for clinical application, constituting a step forward in the development of fast, sensitive and cost-effective diagnostic tools that can improve the current medical care settings of CKD patients.

Trends and Perspectives in Immunosensors for Determination of Currently-Used Pesticides: The Case of Glyphosate, Organophosphates, and Neonicotinoids

Pesticides, due to their intensive use and their peculiar chemical features, can persist in the environment and enter the trophic chain, thus representing an environmental risk for the ecosystems and human health. Although there are several robust and reliable standard analytical techniques for their monitoring, the high frequency of contamination caused by pesticides requires methods for massive monitoring campaigns that are capable of rapidly detecting these compounds in many samples of different origin. Immunosensors represent a potential tool for simple, rapid, and sensitive monitoring of pesticides. Antibodies coupled to electrochemical or optical transducers have resulted in effective detection devices. In this review, the new trends in immunosensor development and the application of immunosensors for the detection of pesticides of environmental concern-such as glyphosate, organophosphates, and neonicotinoids-are described.

Suppressing Non-Specific Binding of Proteins onto Electrode Surfaces in the Development of Electrochemical Immunosensors

Electrochemical immunosensors, EIs, are systems that combine the analytical power of electrochemical techniques and the high selectivity and specificity of antibodies in a solid phase immunoassay for target analyte. In EIs, the most used transducer platforms are screen printed electrodes, SPEs. Some characteristics of EIs are their low cost, portability for point of care testing (POCT) applications, high specificity and selectivity to the target molecule, low sample and reagent consumption and easy to use. Despite all these attractive features, still exist one to cover and it is the enhancement of the sensitivity of the EIs. In this review, an approach to understand how this can be achieved is presented. First, it is necessary to comprise thoroughly all the complex phenomena that happen simultaneously in the protein-surface interface when adsorption of the protein occurs. Physicochemical properties of the protein and the surface as well as the adsorption phenomena influence the sensitivity of the EIs. From this point, some strategies to suppress non-specific binding, NSB, of proteins onto electrode surfaces in order to improve the sensitivity of EIs are mentioned.

Amine-Aldehyde Chemical Conjugation on a Potassium Hydroxide-Treated Polystyrene ELISA Surface for Nanosensing an HIV-p24 Antigen

The enzyme-linked immunosorbent assay (ELISA) has been widely used for disease surveillance and drug screening due to its relatively higher accuracy and sensitivity. Fine-tuning the ELISA is mandatory to elevate the specific detection of biomolecules at a lower abundance. Towards this end, higher molecular capture on the polystyrene (PS) ELISA surface is crucial for efficient detection, and it could be attained by immobilizing the molecules in the correct orientation. It is highly challenging to immobilize protein molecules in a well-aligned manner on an ELISA surface due to charge variations. We employed a 3-(aminopropyl) triethoxysilane (APTES)- and glutaraldehyde (GLU)-coupled PS surface chemical strategy to demonstrate the high performance with ELISA. A potassium hydroxide treatment followed by an equal ratio of 1% APTES and GLU attachment was found to be optimal, and a longer incubation with GLU favored maximum sensitivity. p24 is a vital early secreting antigen for diagnosing human immunodeficiency virus (HIV), and it has been used for efficient detection with the above chemistry. Three different procedures were followed, and they led to the improved detection of the HIV-p24 antigen at 1 nM, which is a 30-fold higher level compared to a conventional ELISA surface. The surface chemical functionalization shown here also displays a higher specificity with human serum and HIV-TAT. The above approach with the designed surface chemistry could also be recommended for disease diagnosis on other sensing surfaces involving the interaction of the probe and the analyte in heterogeneous test samples.

Diagnosing human blood clotting deficiency

There are different clotting factors present in blood, carries the clotting cascade and excessive bleeding may cause a deficiency in the clotting Diagnosis of this deficiency in clotting drastically reduces the potential fatality. For enabling a sensor to detect the clotting factors, suitable probes such as antibody and aptamer have been used to capture these targets on the sensing surface. Two major clotting factors were widely studied for the diagnosis of clotting deficiency, which includes factor IX and thrombin. In addition, factor IX is considered as the substitute for heparin and the prothrombotic associated with the increased thrombin generation are taking into account their prevalence. The biosensors, surface plasmon resonance, evanescent-field-coupled waveguide-mode sensor, metal-enhanced PicoGreen fluorescence and electrochemical aptasensor were well-documented and improvements have been made for high-performance sensing. We overviewed detecting factor IX and thrombin using these biosensors, for the potential application in medical diagnosis.

Surfactant-free Colloidal Particles with Specific Binding Affinity

Colloidal particles with specific binding affinity are essential for in vivo and in vitro biosensing, targeted drug delivery, and micrometer-scale self-assembly. Key to these techniques are surface functionalizations that provide high affinities to specific target molecules. For stabilization in physiological environments, current particle coating methods rely on adsorbed surfactants. However, spontaneous desorption of these surfactants typically has an undesirable influence on lipid membranes. To address this issue and create particles for targeting molecules in lipid membranes, we present here a surfactant-free coating method that combines high binding affinity with stability at physiological conditions. After activating charge-stabilized polystyrene microparticles with EDC/Sulfo-NHS, we first coat the particles with a specific protein and subsequently covalently attach a dense layer of poly(ethyelene) glycol. This polymer layer provides colloidal stability at physiological conditions as well as antiadhesive properties, while the protein coating provides the specific affinity to the targeted molecule. We show that NeutrAvidin-functionalized particles bind specifically to biotinylated membranes and that Concanavalin A-functionalized particles bind specifically to the glycocortex of Dictyostelium discoideum cells. The affinity of the particles changes with protein density, which can be tuned during the coating procedure. The generic and surfactant-free coating method reported here transfers the high affinity and specificity of a protein onto colloidal polystyrene microparticles.

Lab-on-chip systems for integrated bioanalyses

Biomolecular detection systems based on microfluidics are often called lab-on-chip systems. To fully benefit from the miniaturization resulting from microfluidics, one aims to develop 'from sample-to-answer' analytical systems, in which the input is a raw or minimally processed biological, food/feed or environmental sample and the output is a quantitative or qualitative assessment of one or more analytes of interest. In general, such systems will require the integration of several steps or operations to perform their function. This review will discuss these stages of operation, including fluidic handling, which assures that the desired fluid arrives at a specific location at the right time and under the appropriate flow conditions; molecular recognition, which allows the capture of specific analytes at precise locations on the chip; transduction of the molecular recognition event into a measurable signal; sample preparation upstream from analyte capture; and signal amplification procedures to increase sensitivity. Seamless integration of the different stages is required to achieve a point-of-care/point-of-use lab-on-chip device that allows analyte detection at the relevant sensitivity ranges, with a competitive analysis time and cost.