Lab-on-a-chip for multiplexed biosensing of residual antibiotics in milk

Progress and Challenge of Sensors for Dairy Food Safety Monitoring

One of the most consumed foods is milk and milk products, and guaranteeing the suitability of these products is one of the major concerns in our society. This has led to the development of numerous sensors to enhance quality controls in the food chain. However, this is not a simple task, because it is necessary to establish the parameters to be analyzed and often, not only one compound is responsible for food contamination or degradation. To attempt to address this problem, a multiplex analysis together with a non-directed (e.g., general parameters such as pH) analysis are the most relevant alternatives to identifying the safety of dairy food. In recent years, the use of new technologies in the development of devices/platforms with optical or electrochemical signals has accelerated and intensified the pursuit of systems that provide a simple, rapid, cost-effective, and/or multiparametric response to the presence of contaminants, markers of various diseases, and/or indicators of safety levels. However, achieving the simultaneous determination of two or more analytes in situ, in a single measurement, and in real time, using only one working 'real sensor', remains one of the most daunting challenges, primarily due to the complexity of the sample matrix. To address these requirements, different approaches have been explored. The state of the art on food safety sensors will be summarized in this review including optical, electrochemical, and other sensor-based detection methods such as magnetoelastic or mass-based sensors.

Portable self-flowing platform for filtration separation of samples

A portable self-flow filtration and separation platform was designed using soft lithography to create a polydimethylsiloxane (PDMS) microfluidic channel cover combined with a matching acrylic substrate. The separation zone was filled with microbeads of appropriate sizes to achieve universal filtration and separation. This simple structure requires only 20 μl of the sample for filtration separation. A vacuum of 760 torr is applied to the porous PDMS cover to drive the sample during testing. The average time required for a 20 μl sample of blood to pass through the separation zone is about 56 s, while the filling time for the detection zone of volume 6 μl is about 319 s. When the hematocrit of the blood sample is about 20-25%, the separation efficiency is 99.98%. Further, the separation efficiency of fat globules from raw milk is close to 100%, whereas almost all impurities are filtered out from juice and stool samples. It is also observed that E. coli in the stool can pass from the separation to detection zone at a maximum rate of about 81.21%, with an average of about 68.18%.

Biosensing approaches to detect potential milk contaminants: a comprehensive review

Accidentally present contaminants or intentionally added adulterants in milk lead potentially to delivering not only unhealthy but seriously hazardous products. Thorough, fast and sensitive analytical tools are essential for monitoring of milk quality, and for screening of any objectionable contaminants. Biosensors represent an innovative, time-efficient and on-site solution to assess milk quality in addition to their specificity towards target analytes alongside high accuracy within such complex matrices. Most biosensors use antibodies, aptamers or enzymes as the bio-receptor and rely on optical, electrochemical or thermometric transduction to generate a signal. The simplest biosensors appear to be those based on a colorimetric assay, being simple and having a signal that can be detected visually. Electrochemical sensors are more specific and sensitive, though with more complicated designs, whereas thermometric sensors have not been thoroughly explored concerning biosensing contaminants in milk. This review discusses recent advances in the field of biosensors and analyzes the various methods of bio-recognition and transduction with regard to their advantages, limitations, and application to milk products. Additionally, challenges facing further development of these strategies to fulfil the increasing demand for fast and on-line milk quality control are also presented.

Antibiotic residues in milk: Past, present, and future

Now-a-days, various types of antibiotics are being used worldwide in veterinary sector indiscriminately for promotion of growth and treatment of the livestock. Significant portions of antibiotics are released through milk of dairy animals unaltered and exert serious harmful effects on human health. This review evaluates and compare researches on antibiotic residues in milk in published literatures from Pubmed, CrossRef, CAB direct, DOAJ, JournalTOCs, AGRICOLA, ScientificGate, Electronic Journals Library, CAB abstracts, Global Health Databases, Global Impact Factor, Google Scholar, Park Directory of Open Access Journals, BanglaJOL and ISC E-Journals. Antibiotics residue in milk was first detected in 60s and then with an increasing trend with highest after 2,000 (188). The highest no. of works, 49 (21.87%) were accomplished in China, followed by Spain, 30 (13.39%); Germany, 11 (4.91%); and USA, 10 (4.46%). Continent-wise highest researches are published from Europe, 105 (46.88%), followed by Asia, 77 (34.38%); South America, 18 (8.04%); North America, 16 (7.14%); and Africa, 8 (3.57%). For detection, Bovine milk sample is mostly used, 193 (86.16%), followed by ovine, 19 (8.48%); and caprine, 14 (6.25%). Acetonitrile was used in maximum cases (77) for processing the samples. Chromatographic technique was the highest, 115 (51.34%) for detection. Residue of β-lactam group have been detected mostly 133 (36.54%), followed by tetracyclines, 51 (14.01%); fluoroquinolones, 49 (13.46%); sulfonamides, 46 (12.64%); and aminoglycosides, 38 (10.44%). This review observe that antibiotics residues are more common in milk samples that are being manifested in increasing researches on antibiotic detection and measures should adopt to cease this residue.

Methods for field measurement of antibiotic concentrations: limitations and outlook

The growing prevalence of antibiotic resistance poses an increasingly serious threat to human health. Although an important driver of antibiotic resistance is the continuous exposure of bacteria to sublethal concentrations of antibiotics in natural environments, antibiotic pollutants are not currently tracked globally or systematically. This limits the international capacity to address the rise of antibiotic resistance at its source. To address this lack of data, the development of methods to measure antibiotic concentrations on-site is essential. These methods, ideally, must be sensitive to sublethal concentrations of antibiotics and require minimal technical expertise. Furthermore, factors such as cost, selectivity, biosafety and the ability to multiplex must be evaluated in the context of field use. Based on these criteria, we provide a critical review of current methods in antibiotic detection and evaluate their adaptability for use on-site. We categorize these methods into microbiological assays, physical and chemical assays, immunoassays, aptasensors and whole-cell biosensors. We recommend continued development of a dipstick or microfluidics approach with a bacterial promoter-based mechanism and colorimetric output. This technique would incorporate the advantageous aspects of existing methods, maximize shelf-life and ease-of-use, and require minimal resources to implement in the field.

Microchip electrophoresis based aptasensor for multiplexed detection of antibiotics in foods via a stir-bar assisted multi-arm junctions recycling for signal amplification

Microchip electrophoresis (MCE) was a good available method for high-throughput and rapid detecting chemical pollutants in food samples. However, many of the reported MCE assays involve complex design of microchip, laborious operation and poor universality which limited its promotion in multiple antibiotics' detection. Herein, a multiplexed aptasensor was developed based on a universal double-T type microchip to one-step and simultaneously detect several antibiotics within 3 min using chloramphenicol (CAP) and kanamycin (Kana) as representatives. Besides, a novel stir-bar assisted DNA multi-arm junctions recycling (MAJR) strategy was designed for transducing and amplifying the signal. The brief detection mechanism was as following: the added CAP and Kana can specifically react with their aptamer probes on the stir-bar and produce different single-stranded DNA primer, respectively. Afterwards, the primers can trigger MAJR to form a lot of three- and four-arm DNA junctions corresponding to different targets. The DNA multi-arm junctions can be easily separated and detected by MCE for quantification. Moreover, the stir-bar can facilitate phase separation and obviously eliminate matrix interference in food. The assay was successfully applied in milk and fish samples, showing excellent selectivity and sensitivity with a detection limits of 0.52 pg mL^-1 CAP and 0.41 pg mL^-1 Kana (S/N = 3). Thus, the assay holds a great potential application for screening of antibiotics in food.

Detection of low concentrations of ampicillin in milk

Ampicillin, a common antibiotic, is detected at trace concentrations in milk using surface enhanced Raman spectroscopy in a microfluidic device, using less than 20 μL of sample, in 10 minutes, with minimal off-chip preparation. The device is configured so as to favor the interaction of the analyte with colloidal silver, and the optimization of the aggregation of the silver nanoparticles so as to increase the SERS intensity and the consequential sensitivity of analyte detection.

Automated liquid operation method for microfluidic heterogeneous immunoassay

In this work, an automated liquid operation method for multistep heterogeneous immunoassay toward point of care testing (POCT) was proposed. A miniaturized peristaltic pump was developed to control the flow direction, flow time and flow rate in the microliter range according to a program. The peristaltic pump has the advantages of simple structure, small size, low cost, and easy to build and use. By coupling the peristaltic pump with an antibody-coated capillary and a reagent-preloaded cartridge, the complicated liquid handling operation for heterogeneous immunoassay, including sample metering and introduction, multistep reagent introduction and rinsing, could be triggered by an action and accomplished automatically in 12 min. The analytical performance of the present immunoassay system was demonstrated in the measurement of human IgG with fluorescence detection. A detection limit of 0.68 μg/mL IgG and a dynamic range of 2-300 μg/mL were obtained.

Critical issues in sensor science to aid food and water safety

The stability of food and water supplies is widely recognized as a global issue of fundamental importance. Sensor development for food and water safety by nonconventional assays continues to overcome technological challenges. The delicate balance between attaining adequate limits of detection, chemical fingerprinting of the target species, dealing with the complex food matrix, and operating in difficult environments are still the focus of current efforts. While the traditional pursuit of robust recognition methods remains important, emerging engineered nanomaterials and nanotechnology promise better sensor performance but also bring about new challenges. Both advanced receptor-based sensors and emerging non-receptor-based physical sensors are evaluated for their critical challenges toward out-of-laboratory applications.

Nanophotonic lab-on-a-chip platforms including novel bimodal interferometers, microfluidics and grating couplers

One of the main limitations for achieving truly lab-on-a-chip (LOC) devices for point-of-care diagnosis is the incorporation of the "on-chip" detection. Indeed, most of the state-of-the-art LOC devices usually require complex read-out instrumentation, losing the main advantages of portability and simplicity. In this context, we present our last advances towards the achievement of a portable and label-free LOC platform with highly sensitive "on-chip" detection by using nanophotonic biosensors. Bimodal waveguide interferometers fabricated by standard silicon processes have been integrated with sub-micronic grating couplers for efficient light in-coupling, showing a phase resolution of 6.6 × 10(-4)× 2π rad and a limit of detection of 3.3 × 10(-7) refractive index unit (RIU) in bulk. A 3D network of SU-8 polymer microfluidics monolithically assembled at the wafer-level was included, ensuring perfect sealing and compact packaging. To overcome some of the drawbacks inherent to interferometric read-outs, a novel all-optical wavelength modulation system has been implemented, providing a linear response and a direct read-out of the phase variation. Sensitivity, specificity and reproducibility of the wavelength modulated BiMW sensor has been demonstrated through the label-free immunodetection of the human hormone hTSH at picomolar level using a reliable biofunctionalization process.

Recent advances in multiplex immunoassays

The present review reports on the lastest developments in multiplex immunoassays. The selected examples are classified through their detection strategy (fluorescence, chemiluminescence, colorimetry or labeless) and their assay format (standard microtiter plate, polymeric membranes and glass slides). Finally, the degree of integration in a complete system, incorporating fluid handling and detection was also taken into account.

Biosensor applications in the field of antibiotic research--a review of recent developments

Antibacterials are among of the most important medications used in health care. However, their efficacy is increasingly impeded by a tremendous and globally spread bacterial resistance phenomenon. This bacterial resistance is accelerated by inadequate application of antibacterial drugs in humans, the widespread veterinary use of antibacterials, and antibacterial occurrence in the environment and food. Further, there is a lack of development of innovative novel drugs. Therefore, the search for novel antibacterials has to be intensified and the spread of antibacterials in the environment has to be restricted. Due to the fundamental progress in biosensor development and promising applications in the antibiotic field, this review gives for the first time an overview on the use and prospects of biosensor applications in that area. A number of reports have applied biosensors of different design and techniques to search for antibacterials in environmental and foodstuff matrices. These studies are discussed with respect to the analytical values and compared to conventional techniques. Furthermore, biosensor applications to elucidate the mode of action of antimicrobial drugs in vitro have been described. These studies were critically introduced referring to the informational value of those simulations. In summary, biosensors will be illustrated as an innovative and promising, although not yet comprehensively applied, technique in the antibacterial field.

Heterogeneous immunoassays in microfluidic format using fluorescence detection with integrated amorphous silicon photodiodes

Miniaturization of immunoassays through microfluidic technology has the potential to decrease the time and the quantity of reactants required for analysis, together with the potential of achieving multiplexing and portability. A lab-on-chip system incorporating a thin-film amorphous silicon (a-Si:H) photodiode microfabricated on a glass substrate with a thin-film amorphous silicon-carbon alloy directly deposited above the photodiode and acting as a fluorescence filter is integrated with a polydimethylsiloxane-based microfluidic network for the direct detection of antibody-antigen molecular recognition reactions using fluorescence. The model immunoassay used consists of primary antibody adsorption to the microchannel walls followed by its recognition by a secondary antibody labeled with a fluorescent quantum-dot tag. The conditions for the flow-through analysis in the microfluidic format were defined and the total assay time was 30 min. Specific molecular recognition was quantitatively detected. The measurements made with the a-Si:H photodiode are consistent with that obtained with a fluorescence microscope and both show a linear dependence on the antibody concentration in the nanomolar-micromolar range.

Photonics-on-a-chip: recent advances in integrated waveguides as enabling detection elements for real-world, lab-on-a-chip biosensing applications

By leveraging advances in semiconductor microfabrication technologies, chip-integrated optical biosensors are poised to make an impact as scalable and multiplexable bioanalytical measurement tools for lab-on-a-chip applications. In particular, waveguide-based optical sensing technology appears to be exceptionally amenable to chip integration and miniaturization, and, as a result, the recent literature is replete with examples of chip-integrated waveguide sensing platforms developed to address a wide range of contemporary analytical challenges. As an overview of the most recent advances within this dynamic field, this review highlights work from the last 2-3 years in the areas of grating-coupled, interferometric, photonic crystal, and microresonator waveguide sensors. With a focus towards device integration, particular emphasis is placed on demonstrations of biosensing using these technologies within microfluidically controlled environments. In addition, examples of multiplexed detection and sensing within complex matrices--important features for real-world applicability--are given special attention.

Surface plasmon resonance analysis of antibiotics using imprinted boronic acid-functionalized Au nanoparticle composites

Au nanoparticles (NPs) are functionalized with thioaniline electropolymerizable groups and (mercaptophenyl)boronic acid. The antibiotic substrates neomycin (NE), kanamycin (KA), and streptomycin (ST) include vicinal diol functionalities and, thus, bind to the boronic acid ligands. The electropolymerization of the functionalized Au NPs in the presence of NE, KA, or ST onto Au surfaces yields bisaniline-cross-linked Au NP composites that, after removal of the ligated antibiotics, provide molecularly imprinted matrixes which reveal high sensitivities toward the sensing of the imprinted antibiotic analytes (detection limits for analyzing NE, KA, and ST correspond to 2.00 +/- 0.21 pM, 1.00 +/- 0.10 pM, and 200 +/- 30 fM, respectively). The antibiotics are sensed by surface plasmon resonance (SPR) spectroscopy, where the coupling between the localized plasmon of the NPs and the surface plasmon wave associated with the Au surface is implemented to amplify the SPR responses. The imprinted Au NP composites are, then, used to analyze the antibiotics in milk samples.

Label-free immunochemistry approach to detect and identity antibiotics in milk

The rise of antibiotic-resistant bacteria is a major concern for the continued health and well-being of the general population. The widespread use of antibiotics within the farming industry is one of the factors that have been linked to the appearance of these resistant strains. Regulation exists to prevent antibiotic foodstuffs such as milk being distributed to consumers; however, for this to be effective, methods must exist for testing the milk to enforce these regulations. Current techniques are often time consuming and expensive, especially when applied to large number of samples. This has led to an interest in milk analyses, which can be carried out outside the laboratory. The development of immunosensors that exploit the exquisite specificity of antibody binding has been studied, both using labeled antibodies such as ELISA assays and, more recently, label-free approaches that directly detect the presence of the antibiotic on binding to a specific antibody. Within this review, we detail recent advances in the detection of antibiotics, especially in milk, using a variety of methods. Various techniques such as electrochemical and surface plasmon resonance methods are described.

Immunoassays in microfluidic systems

Immunoassays have greatly benefited from miniaturization in microfluidic systems. This review, which summarizes developments in microfluidics-based immunoassays since 2000, includes four sections, focusing on the configurations of immunoassays that have been implemented in microfluidics, the main fluid handling modalities that have been used for microfluidic immunoassays, multiplexed immunoassays in microfluidic platforms, and the emergence of label-free detection techniques. The field of microfluidic immunoassays is continuously improving and has great promise for the future.