Disposable and integrated amperometric immunosensor for direct determination of sulfonamide antibiotics in milk

Novel 6xHis/HaloTag mammalian expressed autoantigens for the detection of humoral response with multiplexed electrochemical biosensors: A breakthrough in colorectal cancer and Alzheimer's disease personalized diagnostics

The integration of autoantibody detection with electrochemical biosensors allows the development of a novel strategy for managing colorectal cancer (CRC) and Alzheimer's disease (AD). This work reports the use, for the first time, of sustainable receptors, autoantigens expressed in mammalian cells, fused to 6xHis at the N-terminus and HaloTag at the C-terminus, immobilized on chloroalkane-modified magnetic beads (MBs) to selectively capture plasma autoantibodies. Detection was based on amperometric measurements using disposable multiplexed screen-printed carbon electrodes (x8 sensing surfaces), horseradish peroxidase (HRP)-conjugated secondary antibodies, and the HQ/H2O2 system. HaloTag immobilization gave rise to a great sensitivity allowing discrimination between patients and healthy individuals in comparison with HisTag or -COOH immobilization. The CRC biosensor integrated seven CRC-specific full-length autoantigens, while the AD bioplatform combined three AD-specific full-length proteins and four AD-specific peptides, which allowed a robust diagnostic performance validated by ROC analyses. These multiplexed biosensors provide minimally invasive, cost-effective, and sustainable alternatives to traditional diagnostic methods, and show ideal for discovery of new targets and for mass screening and early disease detection, supporting personalized medicine approaches.

Electrochemical tracking of gluten in marketed foods by using a recombinant antibody fragment based-platform

The only treatment to effectively manage celiac disease is the avoidance of gluten containing foods. Therefore, and given its high prevalence, it is of utmost importance to have reliable and efficient methods for the detection of gluten to ensure the well-being and quality of life of celiacs. This work presents the development of an electrochemical immunoplatform exhibiting many practical advantages including simplicity, reduced cost and high sensitivity for the screening of gluten-containing products. The methodology exploited the unique features offered by a recombinant antibody fragment with high affinity towards gliadin together with the use of magnetic microcarriers (MμCs) as scaffolds for the implementation of an indirect competitive immunoassay. Using amperometric transduction on disposable electrodes and the horseradish peroxidase/hydrogen peroxide/hydroquinone system, a dynamic range between 7.3 and 1982 ng mL-1 was obtained for gliadin standards, with a limit of detection of 1.4 ng mL-1. The developed immunoplatform was successfully employed for the analysis of a variety of processed foodstuffs, demonstrating the ability to discriminate between gluten-free and gluten-containing foods according to the legislated threshold (20 mg kg-1 of gluten). The agreement with the results provided by the R5-based ELISA and qPCR methods confirmed the suitability of the bioplatform as a competitive tool in terms of assay time (results in just 60 min after gliadin extraction) sensitivity and applicability, even at the point of need.

Tracking Globally 5-Methylcytosine and Its Oxidized Derivatives in Colorectal Cancer Epigenome Using Bioelectroanalytical Technologies

This work presents the first electroanalytical bioplatforms to track individually or simultaneously at a global level all four methylation marks involved in the DNA methylation-demethylation cycle: 5-methylcytosine (5mC) and their sequential oxidative derivatives (5-hydroxymethyl-(5hmC), 5-formyl-(5fC), and 5-carboxyl-(5caC) cytosines). The bioplatforms employed direct competitive immunoassay formats implemented on the surface of magnetic microparticles (MBs) and involved capture antibodies specific to each epimark as well as synthetic biotinylated DNA oligomers with a single epimark that were enzymatically marked with horseradish peroxidase (HRP) to perform an amperometric readout on disposable platforms for single or multiplexed detection. These new electroanalytical biotechnologies, groundbreaking from analytical and clinical perspectives, achieved attractive operational characteristics, reaching detection limits at pM levels for synthetic single epimark-bearing DNA oligomers. The developed methodology was applied to track globally all four target epimarks in a fast, simple, sensitive, and selective way while their correlation in genomic DNA extracted from paired healthy and tumor tissues of patients with colorectal cancer (CRC) was established for the first time.

Advancements in Biosensors for Point-of-Care Testing of Nucleic Acid

Rapid, low-cost and high-specific diagnosis based on nucleic acid detection is pivotal in both detecting and controlling various infectious diseases, effectively curbing their spread. Moreover, the analysis of circulating DNA in whole blood has emerged as a promising noninvasive strategy for cancer diagnosis and monitoring. Although traditional nucleic acid detection methods are reliable, their time-consuming and intricate processes restrict their application in rapid field assays. Consequently, an urgent emphasis on point-of-care testing (POCT) of nucleic acids has arisen. POCT enables timely and efficient detection of specific sequences, acting as a deterrent against infection sources and potential tumor threats. To address this imperative need, it is essential to consolidate key aspects and chart future directions in POCT biosensors development. This review aims to provide an exhaustive and meticulous analysis of recent advancements in POCT devices for nucleic acid diagnosis. It will comprehensively compare these devices across crucial dimensions, encompassing their integrated structures, the synthesized nanomaterials harnessed, and the sophisticated detection principles employed. By conducting a rigorous evaluation of the current research landscape, this review will not only spotlight achievements but also identify limitations, offering valuable insights into the future trajectory of nucleic acid POCT biosensors. Through this comprehensive analysis, the review aspires to serve as an indispensable guide for fostering the development of more potent biosensors, consequently fostering precise and efficient POCT applications for nucleic acids.

Contributing to the management of viral infections through simple immunosensing of the arachidonic acid serum level

A trendsetting direct competitive-based biosensing tool has been developed and implemented for the determination of the polyunsaturated fatty acid arachidonic acid (ARA), a highly significant biological regulator with decisive roles in viral infections. The designed methodology involves a competitive reaction between the target endogenous ARA and a biotin-ARA competitor for the recognition sites of anti-ARA antibodies covalently attached to the surface of carboxylic acid-coated magnetic microbeads (HOOC-MµBs), followed by the enzymatic label of the biotin-ARA residues with streptavidin-horseradish peroxidase (Strep-HRP) conjugate. The resulting bioconjugates were magnetically trapped onto the sensing surface of disposable screen-printed carbon transducers (SPCEs) to monitor the extent of the biorecognition reaction through amperometry. The operational functioning of the exhaustively optimized and characterized immunosensing bioplatform was highly convenient for the quantitative determination of ARA in serum samples from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2-) and respiratory syncytial virus (RSV)-infected individuals in a rapid, affordable, trustful, and sensitive manner.

Electrochemical Biosensors for the Detection of Antibiotics in Milk: Recent Trends and Future Perspectives

Antibiotics have emerged as ground-breaking medications for the treatment of infectious diseases, but due to the excessive use of antibiotics, some drugs have developed resistance to microorganisms. Because of their structural complexity, most antibiotics are excreted unchanged, polluting the water, soil, and natural resources. Additionally, food items are being polluted through the widespread use of antibiotics in animal feed. The normal concentrations of antibiotics in environmental samples typically vary from ng to g/L. Antibiotic residues in excess of these values can pose major risks the development of illnesses and infections/diseases. According to estimates, 300 million people will die prematurely in the next three decades (by 2050), and the WHO has proclaimed "antibiotic resistance" to be a severe economic and sociological hazard to public health. Several antibiotics have been recognised as possible environmental pollutants (EMA) and their detection in various matrices such as food, milk, and environmental samples is being investigated. Currently, chromatographic techniques coupled with different detectors (e.g., HPLC, LC-MS) are typically used for antibiotic analysis. Other screening methods include optical methods, ELISA, electrophoresis, biosensors, etc. To minimise the problems associated with antibiotics (i.e., the development of AMR) and the currently available analytical methods, electrochemical platforms have been investigated, and can provide a cost-effective, rapid and portable alternative. Despite the significant progress in this field, further developments are necessary to advance electrochemical sensors, e.g., through the use of multi-functional nanomaterials and advanced (bio)materials to ensure efficient detection, sensitivity, portability, and reliability. This review summarises the use of electrochemical biosensors for the detection of antibiotics in milk/milk products and presents a brief introduction to antibiotics and AMR followed by developments in the field of electrochemical biosensors based on (i) immunosensor, (ii) aptamer (iii) MIP, (iv) enzyme, (v) whole-cell and (vi) direct electrochemical approaches. The role of nanomaterials and sensor fabrication is discussed wherever necessary. Finally, the review discusses the challenges encountered and future perspectives. This review can serve as an insightful source of information, enhancing the awareness of the role of electrochemical biosensors in providing information for the preservation of the health of the public, of animals, and of our environment, globally.

Electrochemical bioplatform for the determination of the most common and carcinogenic human papillomavirus DNA

Nucleic acid-based analytical bioplatforms have gained importance as diagnostic tests for genomics and as early detection tools for diseases such as cancer. In this context, we report the development of an amperometric bioplatform for the determination of a specific human papillomavirus type 16 (HPV16) sequence. The bioplatform utilizes an immune-nucleic acid hybrid-sandwich assay. A biotinylated RNA capture probe (RNAbCp), complementary to the selected HPV16 target DNA sequence, was immobilised on the surface of streptavidin coated magnetic microbeads (Strep-MBs). The RNA/DNA heteroduplex resulting from the hybridization of the RNAbCP and the HPV16 target sequence was recognised by a commercial antibody that specifically bound to the heteroduplex (Ab_DNA-RNA). A horseradish-peroxide labeled secondary antibody (antiIgG-HRP) was used for the detection of Ab_DNA-RNA. Relying on amperometric detection of the resulting HRP-labeled magnetic bioconjugates captured on screen-printed electrodes (SPCEs) in the presence of H₂O₂ and hydroquinone (HQ), the biotool achieved a low limit of detection (0.5 pM) for the synthetic HPV16 target DNA. In addition, the developed bioplatform was able to discriminate between HPV16 positive and negative human cancer cells using only 25 ng of amplified DNA in a test time of 45 min.

An electrochemical aptasensor for detection of streptomycin based on signal amplification assisted by functionalized gold nanoparticles and hybridization chain reaction

A ratiometric electrochemical aptasensor based on gold nanoparticles (AuNPs) functionalization and hybridization chain reaction (HCR) assisted signal amplification has been for the first time designed for the detection of streptomycin (STR). The double-stranded DNA (dsDNA) formed by the hybridization of ferrocene (Fc)-labeled STR aptamer (Apt) and capture probe (CP) is first immobilized on the gold electrode (GE) surface via Au-S reaction. The specific binding of the target and Apt results in numerous Fc detachment from the sensing interface. Then, the remaining single-stranded CP is combined with AuNPs modified with initiator DNA (iDNA) by auxiliary DNA (aDNA). Among them, the iDNA triggers HCR between two hairpin probes (H1/H2), thus capturing a large number of methylene blue (MB) electrochemical probe, which generates a strong electrochemical signal of MB and a weak electrochemical signal of Fc. Signals are collected by square wave voltammetry (the potential window ranging from -0.5 V to 0.6 V, vs. Ag/AgCl ), and the oxidation peak currents at -0.200 V (MB) and 0.416 V (Fc) are recorded. The use of the ratiometric method has effectively improved the accuracy and reliability of the analysis. The successful application of AuNPs and HCR greatly improves the sensitivity of the sensor, and the detection limit is as low as 0.08 pM. It can sensitively determine STR in the range 0.1 pM to 10 nM. In addition, the designed aptasensor has been successfully applied to the detection of STR in milk and honey samples.

Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met.

Towards Control and Oversight of SARS‐CoV‐2 Diagnosis and Monitoring through Multiplexed Quantitative Electroanalytical Immune Response Biosensors

The development of versatile and sensitive biotools to quantify specific SARS‐CoV‐2 immunoglobulins in SARS‐CoV‐2 infected and non‐infected individuals, built on the surface of magnetic microbeads functionalized with nucleocapsid (N) and in‐house expressed recombinant spike (S) proteins is reported. Amperometric interrogation of captured N‐ and S‐specific circulating total or individual immunoglobulin (Ig) isotypes (IgG, IgM, and IgA), subsequently labelled with HRP‐conjugated secondary antibodies, was performed at disposable single or multiplexed (8×) screen‐printed electrodes using the HQ/HRP/H₂O₂ system. The obtained results using N and in‐house expressed S ectodomains of five SARS‐CoV‐2 variants of concern (including the latest Delta and Omicron) allow identification of vulnerable populations from those with natural or acquired immunity, monitoring of infection, evaluation of vaccine efficiency, and even identification of the variant responsible for the infection.

Towards Control and Oversight of SARS‐CoV‐2 Diagnosis and Monitoring through Multiplexed Quantitative Electroanalytical Immune Response Biosensors

The development of versatile and sensitive biotools to quantify specific SARS‐CoV‐2 immunoglobulins in SARS‐CoV‐2 infected and non‐infected individuals, built on the surface of magnetic microbeads functionalized with nucleocapsid (N) and in‐house expressed recombinant spike (S) proteins is reported. Amperometric interrogation of captured N‐ and S‐specific circulating total or individual immunoglobulin (Ig) isotypes (IgG, IgM, and IgA), subsequently labelled with HRP‐conjugated secondary antibodies, was performed at disposable single or multiplexed (8×) screen‐printed electrodes using the HQ/HRP/H₂O₂ system. The obtained results using N and in‐house expressed S ectodomains of five SARS‐CoV‐2 variants of concern (including the latest Delta and Omicron) allow identification of vulnerable populations from those with natural or acquired immunity, monitoring of infection, evaluation of vaccine efficiency, and even identification of the variant responsible for the infection.

Synthesis of the Magnetically Nanoporous Organic Polymer Fe3O4@SiO2-NH2-COP and Its Application in the Determination of Sulfonamide Residues in Surface Water Surrounding a Cattle Farm

Efficient extractions of trace antibiotic residues in the environment are a key factor for accurate quantification of the residues. A new nanoporous material, namely, magnetically covalent organic polymer (MCOP, Fe₃O₄@SiO₂-NH₂-COP) was synthesized in this work and was used for magnetic solid-phase extraction (MSPE). The combination of MSPE with high-performance liquid chromatography separation together with ultraviolet detection (HPLC-UV) was established as an effective method for the determination of four sulfonamide (SA) residues in surface water surrounding a cattle farm. The synthesized magnetic material was characterized by SEM, TEM, FT-IR, magnetic properties measurement system (MPMS), and nitrogen gas porosimetry. The material possessed many attractive features, such as a unique microporous structure, a larger specific surface area (137.93 m²·g⁻¹) than bare Fe₃O₄ (24.84 m²·g⁻¹), high saturation magnetization (50.5 emu·g⁻¹), open adsorption sites, and high stability. The influencing parameters, including pH, the used amount of MCOPs, the type of eluent, adsorption solution, and desorption time, were optimized. Under the optimized conditions, the method conferred good linearity ranges (R² ≥ 0.9990), low detection limits (S/N = 3, LOD, 0.10–0.25 μg·L⁻¹), and satisfactory recoveries (79.7% to 92.2%). The enrichment factor (EF) for the four SAs was 34.13–38.86. The relative standard deviations of intraday (n = 5) and of interday (n = 3) were less than 4.8% and 8.9%, respectively. The equilibria between extraction and desorption for SAs could be reached within 150 s. The proposed method was sensitive and convenient for detecting SA residues in complex environmental matrices, and the successful application of the new MCOPs as an adsorbent was demonstrated.

Unraveling autoimmune and neurodegenerative diseases by amperometric serological detection of antibodies against aquaporin-4

This work reports the first electroanalytical bioplatform to date for the determination of antibodies against aquaporin-4 (AQP4-Abs), whose serum level is considered as relevant biomarker for certain autoimmune diseases. The bioplatform relies on the use of magnetic microparticles modified with the biotinylated protein for the capture of specific antibodies. The captured IgGs are enzymatically labelled with a secondary antibody conjugated to the horseradish peroxidase (HRP) enzyme. Amperometric transduction is performed using the H2O2/hydroquinone (HQ) system, which results in a cathodic current variation directly proportional to the concentration of the target antibodies. The evaluation of the analytical and operational characteristics of the developed bioplatform shows that it is competitive in terms of sensitivity with the only biosensor reported to date as well as with the commercially available ELISA kits. The achieved limit of detection value is 8.8 pg mL-1. In addition, compared to ELISA kits, the developed bioplatform is advantageous in terms of cost and point of care operation ability. The bioplatform was applied to the analysis of control serum samples with known AQP4-Abs contents as well as of sera from healthy individuals and patients diagnosed with Systemic Lupus Erythematosus (SLE) and Alzheimer (AD) diseases, providing results in agreement with the ELISA methodology.

Electrochemical Methods for the Analysis of Milk

The milk and dairy industries are some of the most profitable sectors in many countries. This business requires close control of product quality and continuous testing to ensure the safety of the consumers. The potential risk of contaminants or degradation products and undesirable chemicals necessitates the use of fast, reliable detection tools to make immediate production decisions. This review covers studies on the application of electrochemical methods to milk (i.e., voltammetric and amperometric) to quantify different analytes, as reported over the last 10 to 15 years. The review covers a wide range of analytes, including allergens, antioxidants, organic compounds, nitrogen- and aldehyde containing compounds, biochemicals, heavy metals, hydrogen peroxide, nitrite, and endocrine disruptors. The review also examines pretreatment procedures applied to milk samples and the use of novel sensor materials. Final perspectives are provided on the future of cost-effective and easy-to-use electrochemical sensors and their advantages over conventional methods.

Multiplexed magnetic beads-assisted amperometric bioplatforms for global detection of methylations in nucleic acids

This work reports the first electrochemical bioplatform developed for the multidetection of 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) in DNA, DNA N6-methyladenine (6mA) and RNA N6-methyladenosine (m6A) methylations at global level. Direct competitive immunoassays were implemented on the surface of magnetic beads (MBs) and optimized for the single amperometric determination of different targets varying in length, sequence and number of methylations on screen-printed carbon electrodes. After evaluating the sensitivity and selectivity of such determinations and the confirmation of no cross-reactivity, a multiplexed disposable platform allowing the simultaneous determination of the mentioned four methylation events in only 45 min has been prepared. The multiplexed bioplatform was successfully applied to the determination of m6A in cellular total RNA and of 5-mC, 5-hmC and 6mA in genomic DNA extracted from tissues. The developed bioplatform showed its usefulness to discriminate the aggressiveness of cancerous cells and between healthy and tumor tissues of colorectal cancer patients.

Electrochemical Immunosensing of ST2: A Checkpoint Target in Cancer Diseases

A magnetic beads (MB)-involved amperometric immunosensor for the determination of ST2, a member of the IL1 receptor family, is reported in this work. The method utilizes a sandwich immunoassay and disposable screen-printed carbon electrodes (SPCEs). Magnetic immunoconjugates built on the surface of carboxylic acid-microsized magnetic particles (HOOC-MBs) were used to selectively capture ST2. A biotinylated secondary antibody further conjugated with a streptavidin peroxidase conjugate (Strep-HRP) was used to accomplish the sandwiching of the target protein. The immune platform exhibits great selectivity and a low limit of detection (39.6 pg mL⁻¹) for ST2, allowing the determination of soluble ST2 (sST2) in plasma samples from healthy individuals and patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) in only 45 min once the immunoconjugates have been prepared. The good correlation of the obtained results with those provided by an ELISA kit performed using the same immunoreagents demonstrates the potential of the developed strategy for early diagnosis and/or prognosis of the fatal PDAC disease.

A colorimetric microfluidic paper-based analytical device for sulfonamides in cow milk using enzymatic inhibition

To increase milk production, antibiotics are administered to animals to provide weight gain and to prevent or treat diseases. The inappropriate use of these substances can lead to antibiotic resistance and allergic reactions and toxic effects to milk consumers. We describe the development of a simple, fast, portable, and low-cost microfluidic paper-based analytical device (μPAD) to quantify sulfonamides in milk using the inhibition of the colorimetric reaction between carbonic anhydrase (CA) and 4-nitrophenyl acetate. The main advantages presented by the μPAD include reproducible batch production, simple application, and precise analysis without previous treatment. The µPAD displayed good linearity (R² ≥ 0.986) in a wide range of sulfonamides in milk (2.5 to 40.0 µmol L^-1), being selective for the drugs even in a highly complex matrix. We expect that this device allows in situ monitoring of milk quality, reducing the prejudicial conditions associated with high concentrations of sulfonamides in milk.

Magnetic microbeads-based amperometric immunoplatform for the rapid and sensitive detection of N6-methyladenosine to assist in metastatic cancer cells discrimination

This work describes the preparation of an immunoplatform for the sensitive and selective determination of N6-methyladenosine (m6A). The simple and fast protocol involves for the first time the use of micromagnetic immunoconjugates to establish a direct competitive assay between the m6A target and a biotinylated RNA oligomer bearing a single m6A enzymatically labelled with a commercial conjugate of streptavidin-peroxidase (Strep-HRP) as tracer. The cathodic current change measured in the presence of H₂O₂/hydroquinone (HQ) at screen-printed carbon electrodes (SPCEs) upon surface capturing the magnetic bioconjugates is inversely proportional to the m6A target concentration. After evaluating the effect of key variables, the analytical characteristics were established for the determination of three different targets: the N6-methyladenosine-5'-triphosphate (m6ATP) ribonucleotide, a short synthetic RNA oligomer bearing a single m6A and the positive control provided in a commercial colorimetric kit for m6A-RNA quantification. The obtained results show that this immunoplatform is competitive with other methods reported to date, achieving an improved sensitivity (limit of detection of 0.9 pM for the short synthetic oligomer) using a much simpler and faster protocol (~1 h) and disposable electrodes for the transduction. Furthermore, the applicability for discriminating the metastatic potential of cancer cells by directly analyzing a small amount of raw total RNA without enriching or fragmenting was also preliminary assessed.

Paper-based point-of-care test with xeno nucleic acid probes

Bridging the unmet need of efficient point-of-care testing (POCT) in biomedical engineering research and practice with the emerging development in artificial synthetic xeno nucleic acids (XNAs), this review summarized the recent development in paper-based POCT using XNAs as sensing probes. Alongside the signal transducing mode and immobilization methods of XNA probes, a detailed evaluation of probe performance was disclosed. With these new aspects, both researchers in synthetic chemistry / biomedical engineering and physicians in clinical practice could gain new insights in designing, manufacturing and choosing suitable reagents and techniques for POCT.

Electrochemical Immunosensors for Antibiotic Detection

Antibiotics are an important class of drugs destined for treatment of bacterial diseases. Misuses and overuses of antibiotics observed over the last decade have led to global problems of bacterial resistance against antibiotics (ABR). One of the crucial actions taken towards limiting the spread of antibiotics and controlling this dangerous phenomenon is the sensitive and accurate determination of antibiotics residues in body fluids, food products, and animals, as well as monitoring their presence in the environment. Immunosensors, a group of biosensors, can be considered an attractive tool because of their simplicity, rapid action, low-cost analysis, and especially, the unique selectivity arising from harnessing the antigen-antibody interaction that is the basis of immunosensor functioning. Herein, we present the recent achievements in the field of electrochemical immunosensors designed to determination of antibiotics.

An electrochemical aptasensor for streptomycin based on covalent attachment of the aptamer onto a mesoporous silica thin film-coated gold electrode

An electrochemical method is described for the determination of streptomycin (STR). It is making use of a gold electrode coated with a thin mesoporous silica film (MSF). In addition, silver nanoparticles were coated on the MSF to increase the surface area, to bind a large amount of aptamer (Apt), and to improve the electrical conductivity. In the presence of STR, it will bind to the Apt and hinder the diffusion of the redox probe hexacyanoferrate through the nanochannels of the mesoporous film. The aptasensor, best operated at a working potential of 0.22 V (vs. Ag/AgCl) has a linear response in the 1 fg.mL^-1 to 6.2 ng.mL^-1 STR concentration range. The detection limit is 0.33 fg.mL^-1. The assay was successfully validated by analyzing spiked samples of milk and blood serum. Graphical abstract Voltammetric assay of streptomycin (STR) by using a Fe(CN)₆^3-/4- probe. The aptamer was immobilized on a gold electrode modified with a mesoporous silica thin film (MSF) that was functionalized with (3-aminopropyl) triethoxysilane (APTES) and silver nanoparticles (AgNP). Incubation with STR leads to a decrease of the current.

Microbial biosensing of ciprofloxacin residues in food by a portable lens-free CCD-based analyzer

We present a rapid and simple approach for sensitive detection of antibiotic residues in food samples based on luminescence induction by live bacterial sensor strains integrated into a CCD-based lens-free optical analyzer (LumiSense). Using ciprofloxacin as a model antibiotic, we demonstrate response times of between 20 and 80 min, and detection thresholds of 8 ng/mL for milk, egg white, and chicken essence, and 64 ng/mL for egg yolk. These values are below the minimal allowed values as defined by European Union regulations. Although not intended to replace traditional analytical equipment and regulation-approved methods, LumiSense and similar systems, sample preparation for which involves only simple mixing, dilution, and homogenization, may nevertheless provide a simple means for high-throughput food sample screening. Graphical abstract Detection of bioluminescence from genetically modified bacteria offers a simple and effective way for monitoring an antibiotic, ciprofloxacin, in milk without prior sample preparation.

Electrochemical immunosensors - A powerful tool for analytical applications

Immunosensors are biosensors based on interactions between an antibody and antigen on a transducer surface. Either antibody or antigen can be the species immobilized on the transducer to detect antigen or antibody, respectively. Because of the strong binding forces between these biomolecules, immunosensors present high selectivity and very high sensitivity, making them very attractive for many applications in different science fields. Electrochemical immunosensors explore measurements of an electrical signal produced on an electrochemical transductor. This signal can be voltammetric, potentiometric, conductometric or impedimetric. Immunosensors utilizing electrochemical detection have been explored in several analyses since they are specific, simple, portable, and generally disposable and can carry out in situ or automated detection. This review addresses the potential of immunosensors destined for application in food and environmental analysis, and cancer biomarker diagnosis. Emphasis is given to the approaches that have been used for construction of electrochemical immunosensors. Additionally, the fundamentals of immunosensors, technology of transducers and nanomaterials and a general overview of the possible applications of electrochemical immunosensors to the food, environmental and diseases analysis fields are described.

Electrochemical Quartz Crystal Nanobalance (EQCN) Based Biosensor for Sensitive Detection of Antibiotic Residues in Milk

An electrochemical quartz crystal nanobalance (EQCN), which provides real-time analysis of dynamic surface events, is a valuable tool for analyzing biomolecular interactions. EQCN biosensors are based on mass-sensitive measurements that can detect small mass changes caused by chemical binding to small piezoelectric crystals. Among the various biosensors, the piezoelectric biosensor is considered one of the most sensitive analytical techniques, capable of detecting antigens at picogram levels. EQCN is an effective monitoring technique for regulation of the antibiotics below the maximum residual limit (MRL). The analysis of antibiotic residues requires high sensitivity, rapidity, reliability and cost effectiveness. For analytical purposes the general approach is to take advantage of the piezoelectric effect by immobilizing a biosensing layer on top of the piezoelectric crystal. The sensing layer usually comprises a biological material such as an antibody, enzymes, or aptamers having high specificity and selectivity for the target molecule to be detected. The biosensing layer is usually functionalized using surface chemistry modifications. When these bio-functionalized quartz crystals are exposed to a particular substance of interest (e.g., a substrate, inhibitor, antigen or protein), binding interaction occurs. This causes a frequency or mass change that can be used to determine the amount of material interacted or bound. EQCN biosensors can easily be automated by using a flow injection analysis (FIA) setup coupled through automated pumps and injection valves. Such FIA-EQCN biosensors have great potential for the detection of different analytes such as antibiotic residues in various matrices such as water, waste water, and milk.