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Since the COVID-19 outbreak was declared a pandemic by the World Health Organization (WHO) in March 2020, ongoing efforts have been made to develop sensitive diagnostic platforms. Detection of viral RNA provides the highest sensitivity and specificity for detection of early and asymptomatic infections. Thus, this work aimed at developing a label-free genosensor composed of graphene as a working electrode that could be embedded into a flex printed circuit board (FPCB) for the rapid, sensitive, amplification-free and label-free detection of SARS-CoV-2. To facilitate liquid handling and ease of use, the developed biosensor was embedded with a user-friendly reservoir chamber. As a proof-of-concept, detection of a synthetic DNA strand matching the sequence of ORF1ab was performed as a two-step strategy involving the immobilization of a biotinylated complementary sequence on a streptavidin-modified surface, followed by hybridization with the target sequence recorded by the differential pulse voltammetric (DPV) technique in the presence of a ferro/ferricyanide redox couple. The effective design of the sensing platform improved its selectivity and sensitivity and allowed DNA quantification ranging from 100 fg/mL to $1~\mu \text{g}$ /mL. Combining the electrochemical technique with FPCB enabled rapid detection of the target sequence using a small volume of the sample (5- $20~\mu \text{L}$ ). We achieved a limit-of-detection of 100 fg/mL, whereas the predicted value was ~33 fg/mL, equivalent to approximately $5\times 10^{5}$ copies/mL and comparable to sensitivities provided by isothermal nucleic acid amplification tests. We believe that the developed approach proves the ability of an FPCB-implemented DNA sensor to act as a potentially simpler and more affordable diagnostic assay for viral infections in Point-Of-Care (POC) applications.

With its origin estimated around December 2019 in Wuhan, China, the ongoing SARS-CoV-2 pandemic is a major global health challenge. The demand for scalable, rapid and sensitive viral diagnostics is thus particularly pressing at present to help contain the rapid spread of infection and prevent overwhelming the capacity of health systems. While high-income countries have managed to rapidly expand diagnostic capacities, such is not the case in resource-limited settings of low- to medium-income countries. Aiming at developing cost-effective viral load detection systems for point-of-care COVID-19 diagnostics in resource-limited and resource-rich settings alike, we report the development of an integrated modular centrifugal microfluidic platform to perform loop-mediated isothermal amplification (LAMP) of viral RNA directly from heat-inactivated nasopharyngeal swab samples. The discs were pre-packed with dried n-benzyl-n-methylethanolamine modified agarose beads used to selectively remove primer dimers, inactivate the reaction post-amplification and allowing enhanced fluorescence detection via a smartphone camera. Sample-to-answer analysis within 1 hour from sample collection and a detection limit of approximately 100 RNA copies in 10 μL reaction volume were achieved. The platform was validated with a panel of 162 nasopharyngeal swab samples collected from patients with COVID-19 symptoms, providing a sensitivity of 96.6% (82.2-99.9%, 95% CI) for samples with Ct values below 26 and a specificity of 100% (90-100%, 95% CI), thus being fit-for-purpose to diagnose patients with a high risk of viral transmission. These results show significant promise towards bringing routine point-of-care COVID-19 diagnostics to resource-limited settings.

Microfluidics has emerged rapidly over the past 20 years and has been investigated for a variety of applications from life sciences to environmental monitoring. Although continuous-flow microfluidics is ubiquitous, segmented-flow or droplet microfluidics offers several attractive features. Droplets can be independently manipulated and analyzed with very high throughput. Typically, microfluidics is carried out within planar networks of microchannels, namely, microfluidic chips. We propose that fibers offer an interesting alternative format with key advantages for enhanced optical coupling. Herein, we demonstrate the generation of monodisperse droplets within a uniaxial optofluidic Lab-in-a-Fiber scheme. We combine droplet microfluidics with laser-induced fluorescence (LIF) detection achieved through the development of an optical side-coupling fiber, which we term a periscope fiber. This arrangement provides stable and compact alignment. Laser-induced fluorescence offers high sensitivity and low detection limits with a rapid response time making it an attractive detection method for in situ real-time measurements. We use the well-established fluorophore, fluorescein, to characterize the Lab-in-a-Fiber device and determine the generation of $$\sim$$ ∼ 0.9 nL droplets. We present characterization data of a range of fluorescein concentrations, establishing a limit of detection (LOD) of 10 nM fluorescein. Finally, we show that the device operates within a realistic and relevant fluorescence regime by detecting reverse-transcription loop-mediated isothermal amplification (RT-LAMP) products in the context of COVID-19 diagnostics. The device represents a step towards the development of a point-of-care droplet digital RT-LAMP platform.

Lab-on-a-chip (LOC) is a well-established microfluidic platform that allows the miniaturization of chemical and biological processes onto a single unit. Minimal sample and reagent consumption, the potential for multiplexing, rapid analysis, and portability are some of the key advantages of LOC. However, the chips typically need to be integrated with bulky and expensive external optics. Alternatively, silica fibers and capillaries offer opportunities for more compact integration of optics with microfluidics while adding advantages such as; flexibility within a high aspect ratio format, uniaxial arrangements, and measurement-at-a-distance.

Label-free approaches to biomolecular detection in microfluidics avoid potential labeling interference, are suitable for the screening of analytes that are not easily tagged, and simplify assay development toward point-of-use applications. In this paper, multimodal label-free detection of biomolecules was performed in a microfluidic system: 1) optically, with an integrated hydrogenated amorphous silicon thin-film photodiode and 2) electrically, using integrated electrochemical impedance interdigitated microelectrodes. Bovine serum albumin, single-stranded DNA, and a mixture of human immunoglobulins G were selected as model biomolecules. The sensitivities of the biomolecular detection were first evaluated in a bare microfluidic channel. The lower limit of detection obtained, for each transducing technique, was 10 nM for the impedimetric detection of ssDNA and 80 nM for the optical detection of a mixture of antibodies. These sensitivities were considered fit-for-purpose when applied to microfluidic systems aimed at monitoring molecular adsorption to different immobilized ligands. To validate the proposed multimodal detection, the model biomolecules were detected in a microfluidic structure packed with ion exchange chromatography agarose microbeads and the target biomolecules were monitored in real time both at bead level and downstream of the packed beads. The application of these label-free sensors ranges from bioprocess optimization to molecular purification and potentially the development of rapid analytics, with the advantages of device compactness, cost effectiveness, high speed of analysis, and multiplexed signal acquisition.

The demand for portable, rapid, sensitive and low-cost DNA detection systems that could be used for rapid diagnostic of disease and infection has greatly motivated the development of new DNA detection platforms in recent years. However, these platforms are often highly complex, requiring an excessively long time of analysis and/or suffer from inadequate sensitivity. Here we report a rapid and simple bead-based microfluidic platform to detect a specific 22-mer DNA sequence via hybridization, serving as a model of a miRNA biomarker for tumor and cardiovascular diseases. Commercial nanoporous chromatography beads were used as solid support for probe DNA immobilization, using either a single-mode electrostatic interaction or multi-mode interactions (electrostatic and hydrophobic). Using a mass balance approach, a probe density of 2.4 × 10 13 ± 18 % ( ± RSD%) molecules/cm2 was quantified in optimized conditions, which was found to provide hybridization efficiencies above 95 % and a hybridization dissociation constant below 1 nM. Comparing targets with different optical labels, namely Atto 430LS, quantum dots and horseradish peroxidase, the lowest limit of detection of 9.5 ± 1.1 pM was achieved with an assay time of 10 min using a quantum dot label coupled with a multi-mode immobilization. These results highlight the potential of the system to be applied as a simple and highly sensitive DNA hybridization platform, achieving low pM sensitivities without the need of a DNA amplification procedure.

In this work, we present the design and fabrication of a fiber device that performs digital droplet microfluidics for molecular diagnostics. A variety of fibers and capillaries were used to build three connected modules dedicated to droplet generation, incubation, and fluorescence detection which enables a uniaxial arrangement. This is in contrast to the traditional 2-dimensional lab-on-a-chip architecture. We characterize our fiber device using a fluorescein dilution series. Our observed detection limit is on the order of 10 nM fluorescein. We demonstrate our all-fiber device for the fluorescence readout after loop-mediated isothermal amplification (LAMP) of synthetic SARS-CoV-2. Our results suggest that this fiber device can successfully distinguish between positive and negative samples in molecular diagnostics. We propose that our fiber device offers benefits over microfluidic chip techniques such as easier optical integration, much simpler sample loading, and faster diagnosis with high specificity and sensitivity.

The detection of pathogens in primary care settings is critical, not only for virus detection but also for the detection of antibiotic resistant bacteria. Microfluidic devices can be used to develop point-of-care detection systems, but are usually insufficiently sensitive for the application. An on-chip isothermal amplification technique, such as the padlock probing-based rolling circle amplification technique, could potentially achieve the desired specificity and sensitivity, while keeping the complexity of the microfluidic device low. In this work, we describe an innovative microfluidic rolling circle amplification performed on microbeads using a continuous flow of solutions with the potential to achieve the required clinical demands in fast and sensitive fashion. Moreover, the integration with amorphous-hydrogenated silicon thin film p-i-n photodiode and a high-pass interference filter to allow the acquisition of the fluorescence signal from the amplification product on-chip, demonstrates the capability of performing the full assay on-chip along with the portability potential of the device.

For microfluidic devices to achieve a practical point-of-need application, it is necessary to circumvent the often excessive system complexity required, such as external pumps and multi-step operation, in order to provide a rapid and simple, while still robust and fit-for-purpose device. We report a simple capillary-based microfluidic device with integrated microbeads and a no-wash, single-step mode of operation that achieves a sub-minute detection of analytes using a fluorescent competitive immunoassay. In particular, minimum detectable limits of 1.7 ng/mL were obtained for mycotoxin detection within 70 s assay time, using 4.5 μL of sample. Furthermore, an internal control was also included in the microfluidic device to provide additional robustness and result validation. These results support the development of ultra-rapid and simple microfluidic devices, easily extended to other relevant targets within the food safety, biomedical or environmental fields.

The optimization of chromatography operating conditions is a lengthy and demanding task that typically requires large volumes of reagents and costly dedicated equipment. In particular, the use of multimodal chromatography, in which multiple interaction groups co-exist in the same ligand, can make the optimization process even more challenging. Nevertheless, the interest in using this emerging type of ligands has been increasing due to the enhanced selectivity and stability demonstrated by multimodal ligands in the purification of several biopharmaceuticals and their lower cost compared to biological affinity ligands. In this work, we report the development of an integrated, regenerable and portable microfluidic platform for performing a rapid screening of chromatography conditions. This platform was tested for the capture of fluorophore-labeled monoclonal antibodies directly from a cell culture supernatant using a multimodal ligand (Capto MMC). Liquid insertion in the microfluidic device was controlled by pneumatically actuated embedded valves and chromatography cycles were monitored via fluorescence measurements using thin-film a-Si:H photodiodes aligned beneath the device. The regeneration of the chromatography micro-column (70 nL) was performed in the end of each cycle, providing repeatable results over several consecutive cycles. Different buffers were successively evaluated in cycles, each cycle having duration of about 3 min, and the different adsorption and elution kinetics were compared, allowing the rapid optimization of conditions to address the capture of the monoclonal antibody from complex media. Overall, a versatile, rapid and relatively inexpensive platform to perform screening studies was developed, providing a high degree of scalability.

Sensitive viral diagnostic methods are increasingly in demand to tackle emerging epidemics. The Zika virus (ZIKV) is particularly relevant in tropical resource limited settings (RLS) and is associated with intermittent epidemics such as the recent 2016 ZIKV outbreak in South America, wherein Zika fever was classified by WHO as a public health emergency of international concern. Thus, there is an urgent need for widespread Zika fever diagnostics and efficient drug therapies. ZIKV diagnostics are typically performed using RT-qPCR in centralized laboratories. While extremely sensitive, RT-qPCR requires rapid heating-cooling cycles, combined with continuous fluorescence measurements to allow quantification, implying high costs and limiting availability of molecular diagnostics in RLS. Here, we report isothermal amplification of ZIKV cDNA using padlock probes followed by two rounds of Rolling Circle Amplification (RCA), termed as circle-to-circle amplification (C2CA), combined with a microfluidic affinity chromatography enrichment (μACE) platform. This platform allowed the detection of

Antibodies and other protein products such as interferons and cytokines are biopharmaceuticals of critical importance which, in order to be safely administered, have to be thoroughly purified in a cost effective and efficient manner. The use of aqueous two-phase extraction (ATPE) is a viable option for this purification, but these systems are difficult to model and optimization procedures require lengthy and expensive screening processes. Here, a methodology for the rapid screening of antibody extraction conditions using a microfluidic channel-based toolbox is presented. A first microfluidic structure allows a simple negative-pressure driven rapid screening of up to 8 extraction conditions simultaneously, using less than 20μL of each phase-forming solution per experiment, while a second microfluidic structure allows the integration of multi-step extraction protocols based on the results obtained with the first device. In this paper, this microfluidic toolbox was used to demonstrate the potential of LYTAG fusion proteins used as affinity tags to optimize the partitioning of antibodies in ATPE processes, where a maximum partition coefficient (K) of 9.2 in a PEG 3350/phosphate system was obtained for the antibody extraction in the presence of the LYTAG-Z dual ligand. This represents an increase of approx. 3.7 fold when compared with the same conditions without the affinity molecule (K=2.5). Overall, this miniaturized and versatile approach allowed the rapid optimization of molecule partition followed by a proof-of-concept demonstration of an integrated back extraction procedure, both of which are critical procedures towards obtaining high purity biopharmaceuticals using ATPE.

For a point-of-use analytical device to be successful in real-world applications, it needs to be rapid, simple to operate and, ideally, able to multiplex the detection of several analytes and samples. Mycotoxin detection in food and feedstock in particular has become increasingly relevant as these toxins, such as ochratoxin A (OTA), aflatoxin B1 (AFB1) and deoxynivalenol (DON), are subject to strict regulations and recommendations in the European Union. A novel, simple, negative pressure-driven device with manually operated magnetic valves was developed and the simultaneous immunodetection of these three mycotoxins was demonstrated via the laminar flow patterning of probes in an area of ≈0.12mm2 and subsequent chemiluminescence generation via HRP-labeled antibodies. The three mycotoxins were detected in less than 20min at concentrations of 100ng/mL for OTA and DON and 3ng/mL for AFB1, spiked in a sample under analysis and simultaneously compared to a toxin-free reference and a standard contaminated with critical target concentrations. The on-chip optical detection was performed in a single acquisition step by integrating a microfabricated array of 25×25µm2 hydrogenated amorphous silicon (a-Si:H) photosensors below the microfluidic chip. The device presented in this work is simple and effective for point-of-use multiplexing of immunoassays and was applied in this work to the screening of mycotoxins.

Immunoassays performed on the nanolitre scale using microfluidics allow a reduction in reagent volumes and assay times, providing, by design, a high degree of control of mass transport and reaction kinetics. Furthermore, the development of rapid microfluidic prototyping technologies including soft lithography, 3D-printing and micromilling have resulted in a dramatic increase in the reporting of innovative analytic strategies integrating sample preparation, immunodetection and signal transduction in miniaturized portable devices. This degree of integration and automation aims to allow the routine monitoring of target molecules by non-specialized personnel. This is currently in high demand by regulatory agencies, producers and consumers within the scope of food safety and quality. This chapter summarizes recent trends in miniaturized immunoassays, discusses the fundamental concepts of immunoassays performed in microfluidic channels and provides an overview of current design strategies for miniaturization, with an emphasis on the integration of optical, electrochemical and label-free methods to provide signal transduction. In addition, examples of these assays in the context of food safety and quality, namely in the detection of low molecular weight organic and inorganic contaminants, protein toxins or allergens and foodborne pathogens, are described and discussed in detail.

Aqueous two-phase extraction (ATPE) has been showing significant potential in the biopharmaceutical industry, allowing the selective separation of high-value proteins directly from unclarified cell culture supernatants. In this context, effective high-throughput screening tools are critical to perform a rapid empirical optimization of operating conditions. In particular, microfluidic ATPE screening devices, coupled with fluorescence microscopy to continuously monitor the partition of fluorophore-labeled proteins, have been recently demonstrated to provide short diffusion distances and rapid partition, using minimal reagent volumes. Nevertheless, the currently overlooked influence of the labeling procedure on partition must be carefully evaluated to validate the extrapolation of results to the unlabeled molecule. Here, three fluorophores with different global charge and reactivity selected to label immunoglobulin G (IgG) at degrees of labeling (DoL) ranging from 0.5 to 7.6. Labeling with BODIPY FL maleimide (DoL = 0.5), combined with tris(2-carboxyethyl) phosphine (TCEP) to generate free thiol groups, is the most promising strategy to minimize the influence of the fluorophore on partition. In particular, the partition coefficient (Kp ) measured in polyethylene glycol (PEG) 3350-phosphate systems with and without the addition of NaCl using microtubes (batch) or microfluidic devices (continuous) is comparable to those quantified for the native protein.

The optimization of chromatography ligands for the purification of biopharmaceuticals is highly demanded to meet the needs of the pharmaceutical industry. In the case of monoclonal antibodies (mAbs), synthetic ligands comprising multiple types of interactions (multimodal) provide process and economic advantages compared to protein-based affinity ligands. However, optimizing the operation window of these ligands requires the development of effective high-throughput screening platforms. Here, a novel microfluidics-based methodology to perform rapid and multiplexed screening of various multimodal ligands relative to their ability to bind different target molecules is demonstrated. The microfluidic structure comprises three individual chambers (≈8 nL each) packed with different types of chromatography beads in series with the feed flow. An artificial mixture composed of immunoglobulin G (IgG) and bovine serum albumin, labeled with different thiol-reactive neutral fluorescent dyes, is used as a model to quantitatively optimize the performance (yield and purity) of the separation. This approach can potentially be used as a predictive analytical tool in the context of mAb purification, allowing low consumption of molecules and providing results in

The rapid and sensitive detection of specific nucleic acid sequences at the point-of-care (PoC) is becoming increasingly in demand for a variety of emergent biomedical applications ranging from infectious disease diagnostics to the screening of antimicrobial resistance. To meet such demand, considerable efforts have been invested towards the development of portable and integrated analytical devices combining microfluidics with miniaturized signal transducers. Here, we demonstrate the combination of rolling circle amplification (RCA)-based nucleic acid amplification with an on-chip size-selective trapping of amplicons on silica beads (~8 nL capture chamber) coupled with a thin-film photodiode (200 × 200 µm area) fluorescence readout. Parameters such as the flow rate of the amplicon solution and trapping time were optimized as well as the photodiode measurement settings, providing minimum detection limits below 0.5 fM of targeted nucleic acids and requiring only 5 μL of pre-amplified sample. Finally, we evaluated the analytical performance of our approach by benchmarking it against a commercial instrument for RCA product (RCP) quantification and further investigated the effect of the number of RCA cycles and elongation times (ranging from 10 to 120 min). Moreover, we provide a demonstration of the application for diagnostic purposes by detecting RNA from influenza and Ebola viruses, thus highlighting its suitability for integrated PoC systems.

The assurance of food and feed safety is one of the major challenges in modern society given the increasing pace at which food commodities are demanded, produced and traded across the globe. Ochratoxin A (OTA), a mycotoxin produced either in the field or during storage, has been increasingly associated with detrimental chronic and acute health implications such as carcinogenicity and hepatotoxicity. Currently, standard certified detection methods include complex and time consuming (>1 h) methodologies based on packed-bed chromatography which must be performed by specialized personnel. However, to effectively monitor mycotoxin levels in crops prior to further processing, either after harvest, during transport or during storage, a rapid, simple, portable and sensitive means of screening is in high demand. In order to meet this demand, a novel ultra-rapid, sensitive (limit-of-detection (LoD)

Aqueous two-phase extraction (ATPE) is a biocompatible liquid-liquid (L-L) separation technique that has been under research for several decades towards the purification of biomolecules, ranging from small metabolites to large animal cells. More recently, with the emergence of rapid-prototyping techniques for fabrication of microfluidic structures with intricate designs, ATPE gained an expanded range of applications utilizing physical phenomena occurring exclusively at the microscale. Today, research is being carried simultaneously in two different volume ranges, mL-scale (microtubes) and nL-scale (microchannels). The objective of this review is to give insight into the state of the art at both microtube and microchannel-scale and to analyze whether miniaturization is currently a competing or divergent technology in a field of applications including bioseparation, bioanalytics, enhanced fermentation processes, catalysis, high-throughput screening and physical/chemical compartmentalization. From our perspective, both approaches are worthy of investigation and, depending on the application, it is likely that either (i) one of the approaches will eventually become obsolete in particular research areas such as purification at the preparative scale or high-throughput screening applications; or (ii) both approaches will function as complementing techniques within the bioanalytics field.

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.

Two novel sandwich-based immunoassays for prostate cancer (PCa) diagnosis are reported, in which the primary antibody for capture is replaced by a DNA aptamer. The assays, which can be performed in parallel, were developed in a microfluidic device and tested for the detection of free Prostate Specific Antigen (fPSA). A secondary antibody (Aptamer–Antibody Assay) or a lectin (Aptamer–Lectin Assay) is used to quantify, by chemiluminescence, both the amount of fPSA and its glycosylation levels. The use of aptamers enables a more reliable, selective and controlled sensing of the analyte. The dual approach provides sensitive detection of fPSA along with selective fPSA glycoprofiling, which is of significant importance in the diagnosis and prognosis of PCa, as tumor progression is associated with changes in fPSA glycosylation. With these approaches, we can potentially detect 0.5 ng/mL of fPSA and 3 ng/mL of glycosylated fPSA using Sambucus nigra (SNA) lectin, both within the relevant clinical range. The approach can be applied to a wide range of biomarkers, thus providing a good alternative to standard antibody-based immunoassays with significant impact in medical diagnosis and prognosis.

Chromatography is a robust purification technique, but requires time-consuming optimization on a case-by-case basis, particularly for monoclonal antibodies (mAbs). This work presents a novel microfluidic platform that significantly speeds up the optimization process and reduces the amount of reagent needed. Binding kinetics for a fluorescent conjugate mAb-Alexa 430 were measured in real time at resin level by integration of the microfluidic chip with 200×200 μm a-Si:H photodiodes on glass substrates aligned with micro-columns. Screening studies were performed using reduced amounts of reagents (∼50 μL), mAb molecules (∼2.5 μL) and resin (∼70 nL) in a rapid (∼2 min/condition) and simple manner.

Food safety can be seriously compromised by the presence of mycotoxins. Their detection becomes increasingly relevant as they are subject to strict regulations in the European Union. To cope with this demand, a novel device with manually operated magnetic valves was developed and applied in a direct competitive immunoassay with multiplexed chemiluminescence detection of ochratoxin A, aflatoxin B1 and deoxynivalenol. The optical detection of chemiluminescence from the enzymatically labelled antibodies is performed with a microfabricated array of 25 μm x 25 μm hydrogenated amorphous silicon (a-Si:H) photoconductors. This strategy provides a simple multiplexing device for mycotoxin screening on the field.

The assurance of strict food safety standards is a major challenge in modern society. Mycotoxins, in particular, are produced by fungi during production, storage or transport, posing serious health concerns to humans and animals. Aiming at developing a point-of-use tool for the rapid detection of mycotoxins at the required regulatory levels, we report a microfluidic ultrafast and single-step fluorescence-based immunoassay, using minimal amounts of reagents. This assay was integrated with 200×200 μm thin-film a-Si:H photodiodes towards a compact detection system. Aflatoxin B1 was detected at 1 ng/mL after 2 min assay time, among the fastest reported in the literature.

Despite significant progress in diagnostics and disease management during the past decades, human immunodeficiency virus (HIV) infections are still responsible for nearly 1 million deaths every year, mostly in resource-limited settings. Thus, novel, accurate and cost-effective tools for viral load monitoring become crucial to allow specific diagnostics and the effective monitoring of the associated antiviral therapies. Herein, we report an effective combination of a (1) padlock probe (PLP)-mediated rolling circle amplification (RCA) bioassay and an (2) agarose bead-based microfluidic device for the affinity chromatography-based capture and detection of RCA products (RCPs) pre-labelled simultaneously with biotin and an organic fluorophore. This method allowed the efficient capture of ~1 μm-sized RCPs followed by their quantification either as discrete signals or an average fluorescence signal, thus being compatible with both high-resolution imaging for maximum sensitivity as well as simpler optical detection setups. A limit of detection30 fM was obtained for HIV-1 synthetic target with just a single round of RCA, comparable to recently reported procedures requiring technically complex amplification strategies such as hyperbranching and/or enzymatic digestion/amplification. Furthermore, targeting a set of five conserved regions in the HIV-1 gag gene, the method could specifically detect HIV-1 in 293T cell culture supernatants, as well as a set of 11 HIV-1 NIH reference samples with four different subtypes. The reported method provides simplicity of operation, unique versatility of signal transduction (i.e. average or discrete signals), and potential coupling with previously reported miniaturized photodetectors. These combined features hold promise for bringing RCA-based molecular diagnostics closer to the point-of-care.

Portable, rapid, cost effective and simple analytical tools are in increasing demand to facilitate the routine monitoring of target chemical/biological compounds at the point-of-need. Such devices are highly relevant within the context of food safety, particularly concerning the screening of highly toxic and strictly regulated mycotoxins. To achieve ultrarapid detection of mycotoxins, namely aflatoxin B1, ochratoxin A and deoxynivalenol, at the point-of-need, a novel multiplexed bead-based microfluidic competitive immunosensor, coupled with an array of a-Si:H thin-film photodiodes for integrated fluorescence signal acquisition, is reported. Simultaneously measuring the initial binding rate for each analyte of the sample under analysis against an internal reference, this device provided limits of detection below 1 ng mL−1 for all mycotoxins in a single-step assay and within 1 minute after mixing the sample under analysis with a fluorescent conjugate. The compatibility of the device with the analysis of mycotoxins spiked in corn samples was further demonstrated after performing a sample preparation procedure based on aqueous two-phase extraction. The short times of analysis and sensitivities in the low ng mL−1 range make these devices potentially competitive with the lateral flow devices that are currently the standard for this application. Furthermore, this device architecture and concept is amenable of being expanded to other analytes in food safety, biomedical and other applications.

The assurance of food and feed safety, including the identification and effective monitoring of multiple biological and chemical hazards, is a major societal challenge, given the increasing pace at which food commodities are demanded, produced and traded across the globe. Within this context, mycotoxins are globally widespread secondary fungal metabolites, which can contaminate crops either in the field or during storage and have serious human and animal health impacts such as carcinogenic, teratogenic and hepatotoxic effects. Therefore, their presence in a wide range of foods and feeds is strictly regulated, particularly in the European Union. In order to perform effective and routine monitoring of mycotoxin levels in the field prior to further processing, during transport or during processing, rapid, simple, portable and sensitive means of screening of regulated mycotoxins are in high demand. This review focuses on (1) discussing the relevance of mycotoxins and the standard approaches for their sampling and monitoring; and (2) compiling and discussing recent advances in miniaturized analytical tools for mycotoxin detection. This provides insights into current research efforts and opportunities to develop a truly integrated and fit-for-purpose analytical tool, suitable for use at critical points of the food, feed and raw material processing and distribution chains.

This paper presents an innovative integrated microfluidic platform which allows an ultrarapid detection of mycotoxins, a prevalent and increasingly monitored class of food contaminants. The simultaneous detection of aflatoxin B1 (AFB1), deoxynivalenol (DON) and ochratoxin A (OTA), within their respective regulatory limits is achieved in a single step within 60 s, by combining an array of thin-film photosensors and a disposable microfluidic device. This platform can potentially be the basis of portable tools allowing routine and cost-effective on-site screening of mycotoxin contamination by non-specialized personnel and be extended to other applications such as biomedical and environmental.

This work presents a simple and innovative approach for the quantitative analysis of optical transduction signals from fluorescence, chemiluminescence and colorimetry coupled to a model affinity interaction inside a microfluidic device. By coupling nanoporous microbeads packed inside a microfluidic channel with an integrated photodetector, it was possible to quantify (i) the specific number of antibody-label conjugates bound to protein A coated beads at increasing concentrations and (ii) the emitted/absorbed photon flux involved in each of the transduction mechanisms. The measurement of (i) and (ii) allows a full quantitative understanding of a biosensing mechanism in general, providing a generic methodology to design a microfluidic point-of-need device with the appropriate label and probe dissociation constant (Kd) to achieve the required sensitivity.

Virus-like particles (VLPs) are promising candidates for a new generation of biopharmaceuticals, with a high impact in gene therapy, vaccination and also in the construction of delivery vehicles. Despite the growing interest in these particles, their production is currently limited by the low capacities and throughputs of classical downstream processing technologies. Aqueous two-phase extraction (ATPE) is a promising bioprocessing technique allowing clarification, concentration and purification to be accomplished in a single step. ATPE also combines a high biocompatibility with a simple and reliable scale-up and can also be performed in a continuous mode of operation. In this work, ATPE conditions for the purification of a Human Immunodeficiency Virus (HIV) VLP were screened and optimized in mL scale batch conditions. Polyethylene glycol (PEG)–salt (potassium phosphate, ammonium sulfate and trisodium citrate) and polymer–polymer (PEG–dextran) systems were investigated, among which the PEG–ammonium sulfate system demonstrated the higher partition coefficient ( K = 4.4). This parameter was then compared with the obtained in a continuous microfluidic setting, performed by flowing both immiscible phases through a 100 width × 20 μm wide microchannel. The batch optimization results showed good agreement with the continuous miniaturized extraction, both in terms of K ( K = 3.9 in microfluidic scale) and protein purity. These novel findings show that PEG–ammonium sulfate ATPE is a promising system for primary HIV-VLP recovery and demonstrate the potential of a miniaturized ATPE for massive parallelization (scale-out) at the preparative scale or integrated in analytical miniaturized systems.

For half a century aqueous two-phase systems (ATPSs) have been applied for the extraction and purification of biomolecules. In spite of their simplicity, selectivity, and relatively low cost they have not been significantly employed for industrial scale bioprocessing. Recently their ability to be readily scaled and interface easily in single-use, flexible biomanufacturing has led to industrial re-evaluation of ATPSs. The purpose of this review is to perform a SWOT analysis that includes a discussion of: (i) strengths of ATPS partitioning as an effective and simple platform for biomolecule purification; (ii) weaknesses of ATPS partitioning in regard to intrinsic problems and possible solutions; (iii) opportunities related to biotechnological challenges that ATPS partitioning may solve; and (iv) threats related to alternative techniques that may compete with ATPS in performance, economic benefits, scale up and reliability. This approach provides insight into the current status of ATPS as a bioprocessing technique and it can be concluded that most of the perceived weakness towards industrial implementation have now been largely overcome, thus paving the way for opportunities in fermentation feed clarification, integration in multi-stage operations and in single-step purification processes.

The field of microfluidics holds great promise for the development of simple and portable lab-on-a-chip systems. The use of capillarity as a means of fluidic manipulation in lab-on-a-chip systems can potentially reduce the complexity of the instrumentation and allow the development of user-friendly devices for point-of-need analyses. In this work, a PDMS microchannel-based, colorimetric, autonomous capillary chip provides a multiplexed and semi-quantitative immunodetection assay. Results are acquired using a standard smartphone camera and analyzed with a simple gray scale quantification procedure. The performance of this device was tested for the simultaneous detection of the mycotoxins ochratoxin A (OTA), aflatoxin B1 (AFB1) and deoxynivalenol (DON) which are strictly regulated food contaminants with severe detrimental effects on human and animal health. The multiplexed assay was performed approximately within 10min and the achieved sensitivities of

The rapid detection of mycotoxins in feed samples is becoming an increasingly relevant challenge for the food production sector, in order to effectively enforce current regulations and assure food and feed safety. To achieve rapid mycotoxin detection, several biosensing strategies have been published, many reaching assay times of the order of a few minutes. However, the vast majority of these rely on sample preparation based on volatile organic solvents, often comprising complex multi-step procedures and devoid of clean-up and/or concentration effects. Here, a novel sample preparation methodology based on a green, non-toxic and inexpensive polyethylene glycol-sodium citrate aqueous two-phase system is reported, providing single-step extraction and concentration of three target mycotoxins within 20min: aflatoxin B1 (AFB1), ochratoxin A (OTA) and deoxynivalenol (DON). With point-of-need applications in mind, the extraction procedure was optimized and validated using a rapid multi-toxin microfluidic competitive immunoassay. The assay was successfully tested with spiked complex solid matrices including corn, soy, chickpea and sunflower-based feeds and limits of detection of 4.6ngg-1±15.8%, 24.1ngg-1±8.1% and 129.7ngg-1±53.1% (±CV) were obtained in corn for AFB1, OTA and DON, respectively. These sensitivities are fit-for-purpose at the required regulatory and recommended limits for animal feed, providing an effective and safe semi-quantitative mycotoxin analysis that can be performed in the field.

This paper describes microbead-based microfluidic systems. Several aspects of bead assays in microfluidics make them advantageous for bioassays in simple microchannels, including enhanced surface-to-volume ratio, improved molecular recognition reaction efficiency, and the wide range of surface functionalization available with commercial microbeads. Two-level SU-8 molds are used to fabricate PDMS microchannels that can hydrodynamically trap different types of microbeads, with characteristic dimensions of tens of microns. The use of these microbead-based microfluidic systems in the biosensing of antibodies, toxins and nucleic acids, as well as in antibody purification will be presented and discussed in this paper.

Multimodal ligands are synthetic molecules comprising multiple types of interactions that have been increasingly used for the capture of different biopharmaceutical compounds within complex biological mixtures. For monoclonal antibodies (mAbs) in particular, these ligands have shown the possibility of direct capture from cell culture supernatants in native conditions, as well as enhanced selectivity and affinity compared to traditional single-mode ligands. However, performing the capture of a target mAb using multimodal chromatography comes with the need for extensive optimization of the operating conditions, due to the multitude of interactions that can be promoted in parallel. In this work, a high-throughput microfluidic platform was developed for the optimization of chromatographic conditions regarding the capture of an anti-interleukin 8 mAb, using a multimodal ligand (2-benzamido-4-mercaptobutanoic acid), under a wide range of buffer pH and conductivities. The interaction of the ligand with the fluorescently labeled target mAb was also analyzed with respect to the individual contribution of the hydrophobic (phenyl) and electrostatic (carboxyl) moieties using fluorescence microscopy. The results were further validated at the macroscale using prepacked columns in standard chromatography assays, and recovery yield values of 94.6% ± 5.2% and 97.7% ± 1.5% were obtained under optimal conditions for the miniaturized and conventional approaches, respectively. In summary, this study highlights that a microfluidic-based approach is a powerful analytical tool to expedite the optimization process while using reduced reagent volumes (

Silicon nanowires are reported for their application in bio sensing area and their potential in the detection of various biomolecules. In the present work, freestanding two-terminal Schottky-barrier silicon nanowire arrays exhibiting memristive behavior are fabricated to obtain Memristive-Biosensors. Scanning electron microscopy reveal details on the morphology of the fabricated structures. The memristive devices are functionalized with anti-free-Prostate Specific Antigen (PSA) antibody by two strategies: a) direct passive adsorption on the device surface, and b) bio-affinity approach using Biotin-Streptavidin combination. The electrical behavior of the so-obtained Memristive-Biosensors is examined dealing with the two systems of bio-functionalization. The presence of biomolecules linked to the surface of the nanostructures is detected by a voltage gap appearing in the memristive electrical characteristics. The system shows the potential for applications in molecular diagnostics especially due to possibilities for detection in the femto molar ranges that allow early detection of the cancer disease.

Thin-film optical transducers integrated in lab-on-a-chip (LoC) devices have the potential to facilitate miniaturization, multiplexing capabilities, portability, and sensitivity. However, there are few systematic studies that provide detailed characterization of these photosensors to particular miniaturized bioassays at reduced light intensities. A more detailed representation of the photosensors performance at low light levels is thus needed in order to improve the engineering of integrated detectors for the next generation of portable biosensors. Here, an assessment of the performance of hydrogenated amorphous silicon (a-Si:H) photosensors, at ultra-low light intensity, based on two different device configurations for integration in a microfluidic platform for biomolecular detection is presented. Both p-i-n photodiodes and parallel contact photoconductors show low dark current density (~10−10 A.cm−2) and photosensitivity comparable with high performing crystalline silicon photosensors. The a-Si:H photosensors were integrated in microfluidic devices for the detection of antibody-horseradish peroxidase conjugates (Ab-HRP) in a chemiluminescence-based assay. Surface concentrations of Ab-HRP as low as ~26 amol.cm−2 and ~9 fmol.cm−2 (corresponding to ~103 and ~106 HRP molecules) were detected with detectors in photodiode and photoconductor configurations, respectively, with the sensitivity of the former being comparable with that of bulky and ultra-sensitive photomultiplier tubes. The excellent sensitivity and dynamic range obtained, together with the miniaturization and arraying potential, highlight the potential of a-Si:H photosensors as an effective means of integrating the multiplexed acquisition of optical data in real time in point-of-need LoC systems.

Immunoassays are fast and sensitive techniques for analyte quantification, and their use in point-of-care devices for medical, environmental, and food safety applications has potential benefits of cost, portability, and multiplexing. However, immunoassays are often affected by matrix interference effects, requiring the use of complex laboratory extraction and concentration procedures in order to achieve the required sensitivity. In this paper we propose an integrated microfluidic device for the simultaneous matrix clean-up, concentration and detection. This device consists of two modules in series, the first performing an aqueous two-phase extraction (ATPE) for matrix extraction and analyte pre-concentration, and the second an immunoassay for quantification. The model analyte was the mycotoxin ochratoxin A (OTA) in a wine matrix. Using this strategy, a limit of detection (LoD) of 0.26 ng mL(-1) was obtained for red wine spiked with OTA, well below the regulatory limit for OTA in wines of 2 ng mL(-1) set by the European Union. Furthermore, the linear response on the logarithmic concentration scale was observed to span 3 orders of magnitude (0.1-100 ng mL(-1)). These results are comparable to those obtained for the quantification of OTA in plain buffer without an integrated ATPE (LoD = 0.15 ng mL(-1)). The proposed method was also found to provide similar results for markedly different matrices, such as red and white wines. This novel approach based on aqueous two-phase systems can help the development of point-of-care devices that can directly deal with real samples in complex matrices without the need for extra extraction processes and equipment.

Immunoassays have a broad application range, from environmental and food toxicology to biomedical analysis, providing rapid and simple methods for analyte quantification. Immunoassays, however, are often challenging at nM and sub nM concentrations and are affected by detrimental matrix interference effects, as is the case of the detection of ochratoxin A (OTA) and Aflatoxin B1 (AFB1). These are widespread mycotoxins found in food and feed, with serious potential implications for human health. This work demonstrates the use of polymer–salt aqueous two phase systems (ATPSs) for the simultaneous concentration of mycotoxins and neutralization of matrix interference. In particular, polyethylene glycol (PEG)-phosphate salt ATPSs were used to enhance the detection sensitivity of OTA and AFB1 in wines and beer by an indirect competitive ELISA. Using this methodology it was possible to quantify both analytes spiked in red wine with limits-of-detection (LoD) down to 0.19 ng/mL and 0.035 ng/mL, respectively, with results comparable to those obtained using solutions of toxins in phosphate buffered saline (PBS) buffer (0.7 ng/mL and 0.009 ng/mL, respectively). Furthermore, a very low matrix-to matrix variability was observed, with LoD and half inhibitory concentration (IC50) values of 5.17 ± 1.08 and 33.2 ± 3.5 ng/mL (±SD) obtained in the detection of OTA spiked in red and white wines, beer or PBS buffer. These results indicate the potential of ATPS as a fast and simple concentration step and in providing matrix-independent analyte quantification for enhanced immunoassay sensitivity below regulatory levels.