The array biosensor: portable, automated systems

Portable Waveguide-Based Optical Biosensor

Rapid, on-site diagnostics allow for timely intervention and response for warfighter support, environmental monitoring, and global health needs. Portable optical biosensors are being widely pursued as a means of achieving fieldable biosensing due to the potential speed and accuracy of optical detection. We recently developed the portable engineered analytic sensor with automated sampling (PEGASUS) with the goal of developing a fieldable, generalizable biosensing platform. Here, we detail the development of PEGASUS's sensing hardware and use a test-bed system of identical sensing hardware and software to demonstrate detection of a fluorescent conjugate at 1 nM through biotin-streptavidin chemistry.

Functionalization of an extended-gate field-effect transistor (EGFET) for bacteria detection

Traditional sensing technologies have drawbacks as they are time-consuming, cost-intensive, and do not attain the required accuracy and reproducibility. Therefore, new methods of measurements are necessary to improve the detection of bacteria. Well-established electrical measurement methods can connect high sensitive sensing systems with biological requirements. One approach is to functionalize an extended-gate field-effect transistor's (EGFET) sensing area with modified porphyrins containing two different linkers. One linker connects the electrode surface with the porphyrin. The other linker bonds bacteria on the functional layer through a specific peptide chain. The negative charge on the surface of the cells regulates the surface potential which has an impact on the electrical behavior of the EGFET. The attendance of attached bacteria on the functionalized sensing area could successfully be detected.

A2BC-Type Porphyrin SAM on Gold Surface for Bacteria Detection Applications: Synthesis and Surface Functionalization

Currently used elaborate technologies for the detection of bacteria can be improved in regard to their time consumption, labor intensity, accuracy and reproducibility. Well-known electrical measurement methods might connect highly sensitive sensing systems with biological requirements. The development of modified sensor surfaces with self-assembled monolayers (SAMs) from functionalized porphyrin for bacteria trapping can lead to a highly sensitive sensor for bacteria detection. Different A₂BC-type porphyrin structures were synthesized and examined regarding their optical behavior. We achieved the synthesis of a porphyrin for SAM formation on a gold surface as electrode material. Two possible bio linkers were attached on the opposite meso-position of the porphyrin, which allows the porphyrin to react as a linker on the surface for bacteria trapping. Different porphyrin structures were attached to a gold surface, the SAM formation and the respective coverage was investigated.

Multiplex Immunoassay Techniques for On-Site Detection of Security Sensitive Toxins

Biological toxins are a heterogeneous group of high molecular as well as low molecular weight toxins produced by living organisms. Due to their physical and logistical properties, biological toxins are very attractive to terrorists for use in acts of bioterrorism. Therefore, among the group of biological toxins, several are categorized as security relevant, e.g., botulinum neurotoxins, staphylococcal enterotoxins, abrin, ricin or saxitoxin. Additionally, several security sensitive toxins also play a major role in natural food poisoning outbreaks. For a prompt response to a potential bioterrorist attack using biological toxins, first responders need reliable, easy-to-use and highly sensitive methodologies for on-site detection of the causative agent. Therefore, the aim of this review is to present on-site immunoassay platforms for multiplex detection of biological toxins. Furthermore, we introduce several commercially available detection technologies specialized for mobile or on-site identification of security sensitive toxins.

In Vivo Detection and Absolute Quantification of a Secreted Bacterial Factor from Skin Using Molecularly Imprinted Polymers in a Surface Plasmon Resonance Biosensor for Improved Diagnostic Abilities

In this study, a surface plasmon resonance (SPR) biosensor was developed for the detection and quantification of a secreted bacterial factor (RoxP) from skin. A molecular imprinting method was used for the preparation of sensor chips and five different monomer-cross-linker compositions were evaluated for sensitivity, selectivity, affinity, and kinetic measurements. The most promising molecularly imprinted polymer (MIP) was characterized by using scanning electron microscopy, atomic force microscopy, and cyclic voltammetry. Limit of detection (LOD) value was calculated as 0.23 nM with an affinity constant of 3.3 × 10^-9 M for the promising MIP. Besides being highly sensitive, the developed system was also very selective for the template protein RoxP, proven by the calculated selectivity coefficients. Finally, absolute concentrations of RoxP in several skin swabs were analyzed by using the developed MIP-SPR biosensor and compared to a competitive ELISA. Consequently, the developed system offers a very efficient tool for the detection and quantification of RoxP as an early indicator for some oxidative skin diseases especially when they are present in low-abundance levels (e.g., skin samples).

EM-Wave Biosensors: A Review of RF, Microwave, mm-Wave and Optical Sensing

This article presents a broad review on optical, radio-frequency (RF), microwave (MW), millimeter wave (mmW) and terahertz (THz) biosensors. Biomatter-wave interaction modalities are considered over a wide range of frequencies and applications such as detection of cancer biomarkers, biotin, neurotransmitters and heart rate are presented in detail. By treating biological tissue as a dielectric substance, having a unique dielectric signature, it can be characterized by frequency dependent parameters such as permittivity and conductivity. By observing the unique permittivity spectrum, cancerous cells can be distinguished from healthy ones or by measuring the changes in permittivity, concentration of medically relevant biomolecules such as glucose, neurotransmitters, vitamins and proteins, ailments and abnormalities can be detected. In case of optical biosensors, any change in permittivity is transduced to a change in optical properties such as photoluminescence, interference pattern, reflection intensity and reflection angle through techniques like quantum dots, interferometry, surface enhanced raman scattering or surface plasmon resonance. Conversely, in case of RF, MW, mmW and THz biosensors, capacitive sensing is most commonly employed where changes in permittivity are reflected as changes in capacitance, through components like interdigitated electrodes, resonators and microstrip structures. In this paper, interactions of EM waves with biomatter are considered, with an emphasis on a clear demarcation of various modalities, their underlying principles and applications.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Streak Imaging Flow Cytometer for Rare Cell Analysis

There is a need for simple and affordable techniques for cytology for clinical applications, especially for point-of-care (POC) medical diagnostics in resource-poor settings. However, this often requires adapting expensive and complex laboratory-based techniques that often require significant power and are too massive to transport easily. One such technique is flow cytometry, which has great potential for modification due to the simplicity of the principle of optical tracking of cells. However, it is limited in that regard due to the flow focusing technique used to isolate cells for optical detection. This technique inherently reduces the flow rate and is therefore unsuitable for rapid detection of rare cells which require large volume for analysis.To address these limitations, we developed a low-cost, mobile flow cytometer based on streak imaging. In our new configuration we utilize a simple webcam for optical detection over a large area associated with a wide-field flow cell. The new flow cell is capable of larger volume and higher throughput fluorescence detection of rare cells than the flow cells with hydrodynamic focusing used in conventional flow cytometry. The webcam is an inexpensive, commercially available system, and for fluorescence analysis we use a 1 W 450 nm blue laser to excite Syto-9 stained cells with emission at 535 nm. We were able to detect low concentrations of stained cells at high flow rates of 10 mL/min, which is suitable for rapidly analyzing larger specimen volumes to detect rare cells at appropriate concentration levels. The new rapid detection capabilities, combined with the simplicity and low cost of this device, suggest a potential for clinical POC flow cytometry in resource-poor settings associated with global health.

Rapid Bacterial Detection via an All-Electronic CMOS Biosensor

The timely and accurate diagnosis of infectious diseases is one of the greatest challenges currently facing modern medicine. The development of innovative techniques for the rapid and accurate identification of bacterial pathogens in point-of-care facilities using low-cost, portable instruments is essential. We have developed a novel all-electronic biosensor that is able to identify bacteria in less than ten minutes. This technology exploits bacteriocins, protein toxins naturally produced by bacteria, as the selective biological detection element. The bacteriocins are integrated with an array of potassium-selective sensors in Complementary Metal Oxide Semiconductor technology to provide an inexpensive bacterial biosensor. An electronic platform connects the CMOS sensor to a computer for processing and real-time visualization. We have used this technology to successfully identify both Gram-positive and Gram-negative bacteria commonly found in human infections.

Improving the Sensitivity and Functionality of Mobile Webcam-Based Fluorescence Detectors for Point-of-Care Diagnostics in Global Health

Resource-poor countries and regions require effective, low-cost diagnostic devices for accurate identification and diagnosis of health conditions. Optical detection technologies used for many types of biological and clinical analysis can play a significant role in addressing this need, but must be sufficiently affordable and portable for use in global health settings. Most current clinical optical imaging technologies are accurate and sensitive, but also expensive and difficult to adapt for use in these settings. These challenges can be mitigated by taking advantage of affordable consumer electronics mobile devices such as webcams, mobile phones, charge-coupled device (CCD) cameras, lasers, and LEDs. Low-cost, portable multi-wavelength fluorescence plate readers have been developed for many applications including detection of microbial toxins such as C. Botulinum A neurotoxin, Shiga toxin, and S. aureus enterotoxin B (SEB), and flow cytometry has been used to detect very low cell concentrations. However, the relatively low sensitivities of these devices limit their clinical utility. We have developed several approaches to improve their sensitivity presented here for webcam based fluorescence detectors, including (1) image stacking to improve signal-to-noise ratios; (2) lasers to enable fluorescence excitation for flow cytometry; and (3) streak imaging to capture the trajectory of a single cell, enabling imaging sensors with high noise levels to detect rare cell events. These approaches can also help to overcome some of the limitations of other low-cost optical detection technologies such as CCD or phone-based detectors (like high noise levels or low sensitivities), and provide for their use in low-cost medical diagnostics in resource-poor settings.

Transforming the blood glucose meter into a general healthcare meter for in vitro diagnostics in mobile health

Recent advances in mobile network and smartphones have provided an enormous opportunity for transforming in vitro diagnostics (IVD) from central labs to home or other points of care (POC). A major challenge to achieving the goal is a long time and high costs associated with developing POC IVD devices in mobile Health (mHealth). Instead of developing a new POC device for every new IVD target, we and others are taking advantage of decades of research, development, engineering and continuous improvement of the blood glucose meter (BGM), including those already integrated with smartphones, and transforming the BGM into a general healthcare meter for POC IVDs of a wide range of biomarkers, therapeutic drugs and other analytical targets. In this review, we summarize methods to transduce and amplify selective binding of targets by antibodies, DNA/RNA aptamers, DNAzyme/ribozymes and protein enzymes into signals such as glucose or NADH that can be measured by commercially available BGM, making it possible to adapt many clinical assays performed in central labs, such as immunoassays, aptamer/DNAzyme assays, molecular diagnostic assays, and enzymatic activity assays onto BGM platform for quantification of non-glucose targets for a wide variety of IVDs in mHealth.

Evanescent wave fluorescence biosensors: Advances of the last decade

Biosensor development has been a highly dynamic field of research and has progressed rapidly over the past two decades. The advances have accompanied the breakthroughs in molecular biology, nanomaterial sciences, and most importantly computers and electronics. The subfield of evanescent wave fluorescence biosensors has also matured dramatically during this time. Fundamentally, this review builds on our earlier 2005 review. While a brief mention of seminal early work will be included, this current review will focus on new technological developments as well as technology commercialized in just the last decade. Evanescent wave biosensors have found a wide array applications ranging from clinical diagnostics to biodefense to food testing; advances in those applications and more are described herein.

Antibody Microarray for E. coli O157:H7 and Shiga Toxin in Microtiter Plates

Antibody microarray is a powerful analytical technique because of its inherent ability to simultaneously discriminate and measure numerous analytes, therefore making the technique conducive to both the multiplexed detection and identification of bacterial analytes (i.e., whole cells, as well as associated metabolites and/or toxins). We developed a sandwich fluorescent immunoassay combined with a high-throughput, multiwell plate microarray detection format. Inexpensive polystyrene plates were employed containing passively adsorbed, array-printed capture antibodies. During sample reaction, centrifugation was the only strategy found to significantly improve capture, and hence detection, of bacteria (pathogenic Escherichia coli O157:H7) to planar capture surfaces containing printed antibodies. Whereas several other sample incubation techniques (e.g., static vs. agitation) had minimal effect. Immobilized bacteria were labeled with a red-orange-fluorescent dye (Alexa Fluor 555) conjugated antibody to allow for quantitative detection of the captured bacteria with a laser scanner. Shiga toxin 1 (Stx1) could be simultaneously detected along with the cells, but none of the agitation techniques employed during incubation improved detection of the relatively small biomolecule. Under optimal conditions, the assay had demonstrated limits of detection of ~5.8 × 10⁵ cells/mL and 110 ng/mL for E. coli O157:H7 and Stx1, respectively, in a ~75 min total assay time.

Programmable bio-nano-chip system: a flexible point-of-care platform for bioscience and clinical measurements

The development of integrated instrumentation for universal bioassay systems serves as a key goal for the lab-on-a-chip community. The programmable bio-nano-chip (p-BNC) system is a versatile multiplexed and multiclass chemical- and bio-sensing system for bioscience and clinical measurements. The system is comprised of two main components, a disposable cartridge and a portable analyzer. The customizable single-use plastic cartridges, which now can be manufactured in high volumes using injection molding, are designed for analytical performance, ease of use, reproducibility, and low cost. These labcard devices implement high surface area nano-structured biomarker capture elements that enable high performance signaling and are index-matched to real-world biological specimens. This detection modality, along with the convenience of on-chip fluid storage in blisters and self-contained waste, represents a standard process to digitize biological signatures at the point-of-care. A companion portable analyzer prototype has been developed to integrate fluid motivation, optical detection, and automated data analysis, and it serves as the human interface for complete assay automation. In this report, we provide a systems-level perspective of the p-BNC universal biosensing platform with an emphasis on flow control, device integration, and automation. To demonstrate the flexibility of the p-BNC, we distinguish diseased and non-case patients across three significant disease applications: prostate cancer, ovarian cancer, and acute myocardial infarction. Progress towards developing a rapid 7 minute myoglobin assay is presented using the fully automated p-BNC system.

Webcam-based flow cytometer using wide-field imaging for low cell number detection at high throughput

Here we describe a novel low-cost flow cytometer based on a webcam capable of low cell number detection in a large volume which may overcome the limitations of current flow cytometry. Several key elements have been combined to yield both high throughput and high sensitivity. The first element is a commercially available webcam capable of 187 frames per second video capture at a resolution of 320 × 240 pixels. The second element in this design is a 1 W 450 nm laser module for area-excitation, which combined with the webcam allows for rapid interrogation of a flow field. The final element is a 2D flow-cell which overcomes the flow limitation of hydrodynamic focusing and allows for higher sample throughput in a wider flow field. This cell allows for the linear velocity of target cells to be lower than in a conventional "1D" hydrodynamic focusing flow-cells typically used in cytometry at similar volumetric flow rates. It also allows cells to be imaged at the full frame rate of the webcam. Using this webcam-based flow cytometer with wide-field imaging, it was confirmed that the detection of fluorescently tagged 5 μm polystyrene beads in "1D" hydrodynamic focusing flow-cells was not practical for low cell number detection due to streaking from the motion of the beads, which did not occur with the 2D flow-cell design. The sensitivity and throughput of this webcam-based flow cytometer was then investigated using THP-1 human monocytes stained with SYTO-9 florescent dye in the 2D flow-cell. The flow cytometer was found to be capable of detecting fluorescently tagged cells at concentrations as low as 1 cell per mL at flow rates of 500 μL min(-1) in buffer and in blood. The effectiveness of detection was concentration dependent: at 100 cells per mL 84% of the cells were detected compared to microscopy, 10 cells per mL 79% detected and 1 cell per mL 59% of the cells were detected. With the blood samples spiked to 100 cells per mL, the average concentration for all samples was 91.4 cells per mL, with a 95% confidence interval of 86-97 cells per mL. These low cell concentrations and the large volume capabilities of the system may overcome the limitations of current cytometry, and are applicable to rare cell (such as circulating tumor cell) detection The simplicity and low cost of this device suggests that it may have a potential use in developing point-of-care clinical flow cytometry for resource-poor settings associated with global health.

Democratization of Nanoscale Imaging and Sensing Tools Using Photonics

Providing means for researchers and citizen scientists in the developing world to perform advanced measurements with nanoscale precision can help to accelerate the rate of discovery and invention as well as improve higher education and the training of the next generation of scientists and engineers worldwide. Here, we review some of the recent progress toward making optical nanoscale measurement tools more cost-effective, field-portable, and accessible to a significantly larger group of researchers and educators. We divide our review into two main sections: label-based nanoscale imaging and sensing tools, which primarily involve fluorescent approaches, and label-free nanoscale measurement tools, which include light scattering sensors, interferometric methods, photonic crystal sensors, and plasmonic sensors. For each of these areas, we have primarily focused on approaches that have either demonstrated operation outside of a traditional laboratory setting, including for example integration with mobile phones, or exhibited the potential for such operation in the near future.

Cell streak imaging cytometry for rare cell detection

Detection of rare cells, such as circulating tumor cells, have many clinical applications. To measure rare cells with increased sensitivity and improved data managements, we developed an imaging flow cytometer with a streak imaging mode capability. The new streak mode imaging mode utilizes low speed video to capture moving fluorescently labeled cells in a flow cell. Each moving cell is imaged on multiple pixels on each frame, where the cell path is marked as a streak line proportional to the length of the exposure. Finding rare cells (e.g., <1 cell/mL) requires measuring larger sample volumes to achieve higher sensitivity, therefore we combined streak mode imaging with a "wide" high throughput flow cell (e.g. flow rates set to 10 mL/min) in contrast to the conventional "narrow" hydrodynamic focusing cells typically used in cytometry that are inherently limited to low flow rates. The new flow cell is capable of analyzing 20 mL/min of fluorescently labeled cells. To further increase sensitivity, the signal to noise ratio of the images was also enhanced by combining three imaging methods: (1) background subtraction, (2) pixel binning, and (3) CMOS color channel selection. The streaking mode cytometer has been used for the analysis of SYTO-9 labeled THP-1 human monocytes in buffer and in blood. Samples of cells at 1 cell/mL and 0.1 cell/mL were analyzed in 30 mL with flow rates set to 10 mL/min and frame rates of 4 fps (frame per second). For the target of 1 cell/mL, an average concentration of 0.91 cell/mL was measured by cytometry, with a standard error of 0.03 (C(95) = 0.85-0.97). For the target of 0.1 cell/mL, an average concentration of 0.083 cell/mL was measured, with a standard error of 0.01 (C(95) = 0.065-0.102). Whole blood was also spiked with SYTO-9 labeled cells to a concentration of 10 cell/mL, and the average flow cytometry measurement was 8.7 cells/mL (i.e. 0.87 cells/mL in diluted blood) with a 95% CL of 8.1-9.2 cells/mL. This demonstrated the ability to detect rare cells in blood with high accuracy. Such detection approaches for rare cells have many potential clinical applications. Furthermore, the simplicity and low cost of this device may enable expansion of cell-based clinical diagnostics, especially in resource-poor settings.

Mobile flow cytometer for mHealth

Flow cytometry is used for cell counting and analysis in numerous clinical and environmental applications. However flow cytometry is not used in mHealth mainly because current flow cytometers are large, expensive, power-intensive devices designed to operate in a laboratory. Their design results in a lack of portability and makes them unsuitable for mHealth applications. Another limitation of current technology is the low volumetric throughput rates that are not suitable for rapid detection of rare cells.To address these limitations, we describe here a novel, low-cost, mobile flow cytometer based on wide-field imaging with a webcam for large volume and high throughput fluorescence detection of rare cells as a simulation for circulating tumor cells (CTCs) detection. The mobile flow cytometer uses a commercially available webcam capable of 187 frames per second video capture at a resolution of 320 × 240 pixels. For fluorescence detection, a 1 W 450 nm blue laser is used for excitation of Syto-9 fluorescently stained cells detected at 535 nm. A wide-field flow cell was developed for large volume analysis that allows for the linear velocity of target cells to be lower than in conventional hydrodynamic focusing flow cells typically used in cytometry. The mobile flow cytometer was found to be capable of detecting low concentrations at flow rates of 500 μL/min, suitable for rare cell detection in large volumes. The simplicity and low cost of this device suggests that it may have a potential clinical use for mHealth flow cytometry for resource-poor settings associated with global health.

A graphene oxide based fluorescence resonance energy transfer (FRET) biosensor for ultrasensitive detection of botulinum neurotoxin A (BoNT/A) enzymatic activity

Botulinum neurotoxins (BoNTs) are among the most potent toxic bacterial proteins for humans, which make them potential agents for bioterrorism. Therefore, an ultrasensitive detection of BoNTs and their active states is in great need as field-deployable systems for anti-terrorism applications. We report the construction of a novel graphene oxide (GO)-peptide based fluorescence resonance energy transfer (FRET) biosensor for ultrasensitive detection of the BoNT serotype A light chain (BoNT-LcA) protease activity. A green fluorescence protein (GFP) modified SNAP-25 peptide substrate (SNAP-25-GFP) was optimally designed and synthesized with the centralized recognition/cleavage sites. This FRET platform was constructed by covalent immobilization of peptide substrate on GO with BSA passivation which have advantages of low non-specific adsorption and high stability in protein abundant solution. BoNT-LcA can specifically cleave SNAP-25-GFP substrate covalently immobilized on GO to release the fragment with GFP. Based on fluorescence signal recovery measurement, the target BoNT-LcA was detected sensitively and selectively with the linear detection range from 1fg/mL to 1pg/mL. The limit of detection (LOD) for BoNT-LcA is around 1fg/mL.

Development of an ELISA microarray assay for the sensitive and simultaneous detection of ten biodefense toxins

Plant and microbial toxins are considered bioterrorism threat agents because of their extreme toxicity and/or ease of availability. Additionally, some of these toxins are increasingly responsible for accidental food poisonings. The current study utilized an ELISA-based protein antibody microarray for the multiplexed detection of ten biothreat toxins, botulinum neurotoxins (BoNT) A, B, C, D, E, F, ricin, shiga toxins 1 and 2 (Stx), and staphylococcus enterotoxin B (SEB), in buffer and complex biological matrices. The multiplexed assay displayed a sensitivity of 1.3 pg mL(-1) (BoNT/A, BoNT/B, SEB, Stx-1 and Stx-2), 3.3 pg mL(-1) (BoNT/C, BoNT/E, BoNT/F) and 8.2 pg mL(-1) (BoNT/D, ricin). All assays demonstrated high accuracy (75-120 percent recovery) and reproducibility (most coefficients of variation <20%). Quantification curves for the ten toxins were also evaluated in clinical samples (serum, plasma, nasal fluid, saliva, stool, and urine) and environmental samples (apple juice, milk and baby food) with overall minimal matrix effects. The multiplex assays were highly specific, with little cross-reactivity observed between the selected toxin antibodies. The results demonstrate a multiplex microarray that improves current immunoassay sensitivity for biological warfare agents in buffer, clinical, and environmental samples.

Biosensors for whole-cell bacterial detection

Bacterial pathogens are important targets for detection and identification in medicine, food safety, public health, and security. Bacterial infection is a common cause of morbidity and mortality worldwide. In spite of the availability of antibiotics, these infections are often misdiagnosed or there is an unacceptable delay in diagnosis. Current methods of bacterial detection rely upon laboratory-based techniques such as cell culture, microscopic analysis, and biochemical assays. These procedures are time-consuming and costly and require specialist equipment and trained users. Portable stand-alone biosensors can facilitate rapid detection and diagnosis at the point of care. Biosensors will be particularly useful where a clear diagnosis informs treatment, in critical illness (e.g., meningitis) or to prevent further disease spread (e.g., in case of food-borne pathogens or sexually transmitted diseases). Detection of bacteria is also becoming increasingly important in antibioterrorism measures (e.g., anthrax detection). In this review, we discuss recent progress in the use of biosensors for the detection of whole bacterial cells for sensitive and earlier identification of bacteria without the need for sample processing. There is a particular focus on electrochemical biosensors, especially impedance-based systems, as these present key advantages in terms of ease of miniaturization, lack of reagents, sensitivity, and low cost.

Immunoassays and biosensors for the detection of cyanobacterial toxins in water

Algal blooms are a frequent phenomenon in nearly all kinds of fresh water. Global warming and eutrophication by waste water, air pollution and fertilizers seem to lead to an increased frequency of occurrence. Many cyanobacteria produce hazardous and quite persistent toxins, which can contaminate the respective water bodies. This may limit the use of the raw water for many purposes. The purification of the contaminated water might be quite costly, which makes a continuous and large scale treatment economically unfeasible in many cases. Due to the obvious risks of algal toxins, an online or mobile detection method would be highly desirable. Several biosensor systems have been presented in the literature for this purpose. In this review, their mode of operation, performance and general suitability for the intended purpose will be described and critically discussed. Finally, an outlook on current developments and future prospects will be given.

Early lung cancer diagnosis by biosensors

Lung cancer causes an extreme threat to human health, and the mortality rate due to lung cancer has not decreased during the last decade. Prognosis or early diagnosis could help reduce the mortality rate. If microRNA and tumor-associated antigens (TAAs), as well as the corresponding autoantibodies, can be detected prior to clinical diagnosis, such high sensitivity of biosensors makes the early diagnosis and prognosis of cancer realizable. This review provides an overview of tumor-associated biomarker identifying methods and the biosensor technology available today. Laboratorial researches utilizing biosensors for early lung cancer diagnosis will be highlighted.

Campylobacter spp. detection in the 21st century: a review of the recent achievements in biosensor development

Campylobacter spp. are an important cause of acute bacterial diseases in humans worldwide. Many bacterial species in the Campylobacter genus are considered harmful and may cause several infectious diseases. Currently, there are no commercial biosensors available to detect Campylobacter spp. in food matrices, and little to no testing has been done in research laboratories with actual food matrices. Biosensors potentially provide a powerful means to detect Campylobacter spp. with the advantages of high sensitivity (low limits of detection with a high signal to noise ratio), high specificity (able to selectively detect the target among several similar targets), real time sensing, and in-site monitoring. This review summarizes the latest research in biosensing technologies for detection of Campylobacter spp. based on a variety of transducers and recognition elements. Finally, a comparison is made among all recently reported biosensors for the detection of Campylobacter spp.

A high-throughput antibody-based microarray typing platform

Many rapid methods have been developed for screening foods for the presence of pathogenic microorganisms. Rapid methods that have the additional ability to identify microorganisms via multiplexed immunological recognition have the potential for classification or typing of microbial contaminants thus facilitating epidemiological investigations that aim to identify outbreaks and trace back the contamination to its source. This manuscript introduces a novel, high throughput typing platform that employs microarrayed multiwell plate substrates and laser-induced fluorescence of the nucleic acid intercalating dye/stain SYBR Gold for detection of antibody-captured bacteria. The aim of this study was to use this platform for comparison of different sets of antibodies raised against the same pathogens as well as demonstrate its potential effectiveness for serotyping. To that end, two sets of antibodies raised against each of the "Big Six" non-O157 Shiga toxin-producing E. coli (STEC) as well as E. coli O157:H7 were array-printed into microtiter plates, and serial dilutions of the bacteria were added and subsequently detected. Though antibody specificity was not sufficient for the development of an STEC serotyping method, the STEC antibody sets performed reasonably well exhibiting that specificity increased at lower capture antibody concentrations or, conversely, at lower bacterial target concentrations. The favorable results indicated that with sufficiently selective and ideally concentrated sets of biorecognition elements (e.g., antibodies or aptamers), this high-throughput platform can be used to rapidly type microbial isolates derived from food samples within ca. 80 min of total assay time. It can also potentially be used to detect the pathogens from food enrichments and at least serve as a platform for testing antibodies.

Charged-coupled device (CCD) detectors for Lab-on-a Chip (LOC) optical analysis

A critical element of any Lab-on-a-Chip (LOC) is a detector; among the many detection approaches, optical detection is very widely used for biodetection. One challenge for advancing the development of LOC for biodetection has been to enhance the portability and lower the cost for Point-of-Care diagnostics, which has the potential to enhance the quality of healthcare delivery for underserved populations and for global health. We describe a simple and relatively low cost charged-coupled device (CCD)-based detector that can be integrated with a conventional microtiter plate or a portable LOC assay for various optical detection modalities including fluorescence, chemiluminescence, densitometry, and colorimetric assays. In general, the portable battery-operated CCD-based detection system consists of four modules: (1) a cooled CCD digital camera to monitor light emission, (2) a LOC or microtiter plate to perform assays, (3) a light source to illuminate the assay (such as electroluminescence (EL) or light emitting diode (LED)), and (4) a portable computer to acquire and analyze images. The configuration of the fluorescence detector presented here was designed to measure fluorogenic excitation at 490 nm and to monitor emission at 523 nm used for FITC detection.The LOC used for this detection system was fabricated with laminated object manufacturing (LOM) technology, and was designed to detection activity of botulinum neurotoxin serotype A (BoNT-A) using a fluorogenic peptide substrate (SNAP-25) for botulinum neurotoxin serotype A (BoNT-A) labeled with FITC. The limit of detection (LOD) for the CCD detector is 0.5 nM (25 ng/ml). The portable system is small and is powered by a 12 V source. The modular detector was designed with easily interchangeable LEDs, ELs, filters, lenses, and LOC, and can be used and adapted for a wide variety of densitometry, florescence and colorimetric assays.

An ELISA Lab-on-a-Chip (ELISA-LOC)

Laminated object manufacturing (LOM) technology using polymer sheets is an easy and affordable method for rapid prototyping of Lab-on-a-Chip (LOC) systems. It has recently been used to fabricate a miniature 96 sample ELISA lab-on-a-chip (ELISA-LOC) by integrating the washing step directly into an ELISA plate. LOM has been shown to be capable of creating complex 3D microfluidics through the assembly of a stack of polymer sheets with features generated by laser micromachining and by bonding the sheets together with adhesive. A six layer ELISA-LOC was fabricated with an acrylic (poly(methyl methacrylate) (PMMA)) core and five polycarbonate layers micromachined by a CO(2) laser with simple microfluidic features including a miniature 96-well sample plate. Immunological assays can be carried out in several configurations (1 × 96 wells, 2 × 48 wells, or 4 × 24 wells). The system includes three main functional elements: (1) a reagent loading fluidics module, (2) an assay and detection wells plate, and (3) a reagent removal fluidics module. The ELISA-LOC system combines several biosensing elements: (1) carbon nanotube (CNT) technology to enhance primary antibody immobilization, (2) sensitive ECL (electrochemiluminescence) detection, and (3) a charge-coupled device (CCD) detector for measuring the light signal generated by ECL. Using a sandwich ELISA assay, the system detected Staphylococcal enterotoxin B (SEB) at concentrations as low as 0.1 ng/ml, a detection level similar to that reported for conventional ELISA. ELISA-LOC can be operated by a syringe and does not require power for operation. This simple point-of-care (POC) system is useful for carrying out various immunological assays and other complex medical assays without the laboratory required for conventional ELISA, and therefore may be more useful for global healthcare delivery.

Microfluidic assay without blocking for rapid HIV screening and confirmation

The essential step for HIV spreading limitation is the screening tests. However, there are multiple disadvantages in current screening assays which need further confirmation test. Herein we developed a rapid HIV assay combining screening and confirmation test by using the microfluidic network assay. Meanwhile, the assay is accelerated by bypassing the step of blocking. We call this method as microfluidic assay without blocking (MAWB). Both the limit of detection and reagent incubation time of MAWB are determined by screening of one model protein pair: ovalbumin and its antibody. The assay time is accelerated about 25% while the limit of detection (LOD) is well kept. Formatting the method in for both HIV screening (testing 8 HIV-related samples) and confirmation (assaying 6 kinds of HIV antibodies of each sample) within 30 min was successful. Fast HIV screening and confirmation of 20 plasma samples were also demonstrated by this method. MAWB improved the assay speed while keeping the LOD of conventional ELISA. Meanwhile, both the accuracy and throughput of MAWB were well improved, which made it an excellent candidate for a quick HIV test for both screening and confirmation. Methods like this one will find wide applications in clinical diagnosis and biochemical analysis based on the interactions between pairs of molecules.

Multiplex fiber optic biosensor for detection of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica from ready-to-eat meat samples

Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica are the most common foodborne bacterial pathogens and are responsible for many outbreaks. Therefore, multiplex detection of these three using a single assay platform is highly desirable. The objective was to develop and optimize a fiber optic sensor for simultaneous detection of these three from food. The streptavidin coated optical waveguides were immobilized with biotinylated polyclonal antibodies and exposed to the bacterial suspensions or enriched food samples for 2 h. Pathogens were detected after reacting with Alexa-Fluor 647-labeled monoclonal antibodies. Ready-to-eat beef, chicken and turkey meats were inoculated with each pathogen (~100 cfu/25 g), enriched in SEL (Salmonella, E. coli, Listeria), a multipathogen selective enrichment broth for 18 h and tested with the biosensor. The biosensor was able to detect each pathogen, individually or in a mixture with very little cross-reactivity. The limit of detection for the sensor was ~10(3) cfu/ml for all three pathogens. Furthermore, the biosensor successfully detected each pathogen, grown in a mixture from enriched meat samples under 24 h. The pathogen presence was further verified by PCR and immunofluorescence assay. The multiplex fiber optic sensor shows promise for detection of the three pathogens if present in the same sample eliminating the use of multiple single pathogen detection platforms.

Biosensors for the analysis of microbiological and chemical contaminants in food

Increases in food production and the ever-present threat of food contamination from microbiological and chemical sources have led the food industry and regulators to pursue rapid, inexpensive methods of analysis to safeguard the health and safety of the consumer. Although sophisticated techniques such as chromatography and spectrometry provide more accurate and conclusive results, screening tests allow a much higher throughput of samples at a lower cost and with less operator training, so larger numbers of samples can be analysed. Biosensors combine a biological recognition element (enzyme, antibody, receptor) with a transducer to produce a measurable signal proportional to the extent of interaction between the recognition element and the analyte. The different uses of the biosensing instrumentation available today are extremely varied, with food analysis as an emerging and growing application. The advantages offered by biosensors over other screening methods such as radioimmunoassay, enzyme-linked immunosorbent assay, fluorescence immunoassay and luminescence immunoassay, with respect to food analysis, include automation, improved reproducibility, speed of analysis and real-time analysis. This article will provide a brief footing in history before reviewing the latest developments in biosensor applications for analysis of food contaminants (January 2007 to December 2010), focusing on the detection of pathogens, toxins, pesticides and veterinary drug residues by biosensors, with emphasis on articles showing data in food matrices. The main areas of development common to these groups of contaminants include multiplexing, the ability to simultaneously analyse a sample for more than one contaminant and portability. Biosensors currently have an important role in food safety; further advances in the technology, reagents and sample handling will surely reinforce this position.

Image stacking approach to increase sensitivity of fluorescence detection using a low cost complementary metal-oxide-semiconductor (CMOS) webcam

Optical technologies are important for biological analysis. Current biomedical optical analyses rely on high-cost, high-sensitivity optical detectors such as photomultipliers, avalanched photodiodes or cooled CCD cameras. In contrast, Webcams, mobile phones and other popular consumer electronics use lower-sensitivity, lower-cost optical components such as photodiodes or CMOS sensors. In order for consumer electronics devices, such as webcams, to be useful for biomedical analysis, they must have increased sensitivity. We combined two strategies to increase the sensitivity of CMOS-based fluorescence detector. We captured hundreds of low sensitivity images using a Webcam in video mode, instead of a single image typically used in cooled CCD devices.We then used a computational approach consisting of an image stacking algorithm to remove the noise by combining all of the images into a single image. While video mode is widely used for dynamic scene imaging (e.g. movies or time-lapse photography), it is not used to capture a single static image, which removes noise and increases sensitivity by more than thirty fold. The portable, battery-operated Webcam-based fluorometer system developed here consists of five modules: (1) a low cost CMOS Webcam to monitor light emission, (2) a plate to perform assays, (3) filters and multi-wavelength LED illuminator for fluorophore excitation, (4) a portable computer to acquire and analyze images, and (5) image stacking software for image enhancement. The samples consisted of various concentrations of fluorescein, ranging from 30 μM to 1000 μM, in a 36-well miniature plate. In the single frame mode, the fluorometer's limit-of-detection (LOD) for fluorescein is ∼1000 μM, which is relatively insensitive. However, when used in video mode combined with image stacking enhancement, the LOD is dramatically reduced to 30 μM, sensitivity which is similar to that of state-of-the-art ELISA plate photomultiplier-based readers. Numerous medical diagnostics assays rely on optical and fluorescence readers. Our novel combination of detection technologies, which is new to biodetection may enable the development of new low cost optical detectors based on an inexpensive Webcam (<$10). It has the potential to form the basis for high sensitivity, low cost medical diagnostics in resource-poor settings.

Multiplex bioanalytical methods for food and environmental monitoring

Recent advances in miniaturization of analytical systems and newly emerging technologies offer platforms with greater automation and multiplexing capabilities than traditional biological binding assays. Multiplexed bioanalytical techniques provide control agencies and food industries with new possibilities for improved, more efficient monitoring of food and environmental contaminants. This review deals with recent developments in planar-array and suspension-array technologies, and their applications in detecting pathogens, food allergens and adulterants, toxins, antibiotics and environmental contaminants.

CMOS Imaging of Temperature Effects on Pin-Printed Xerogel Sensor Microarrays

In this paper, we study the effect of temperature on the operation and performance of a xerogel-based sensor microarrays coupled to a complementary metal-oxide semiconductor (CMOS) imager integrated circuit (IC) that images the photoluminescence response from the sensor microarray. The CMOS imager uses a 32 × 32 (1024 elements) array of active pixel sensors and each pixel includes a high-gain phototransistor to convert the detected optical signals into electrical currents. A correlated double sampling circuit and pixel address/digital control/signal integration circuit are also implemented on-chip. The CMOS imager data are read out as a serial coded signal. The sensor system uses a light-emitting diode to excite target analyte responsive organometallic luminophores doped within discrete xerogel-based sensor elements. As a proto type, we developed a 3 × 3 (9 elements) array of oxygen (O2) sensors. Each group of three sensor elements in the array (arranged in a column) is designed to provide a different and specific sensitivity to the target gaseous O2 concentration. This property of multiple sensitivities is achieved by using a mix of two O2 sensitive luminophores in each pin-printed xerogel sensor element. The CMOS imager is designed to be low noise and consumes a static power of 320.4 μW and an average dynamic power of 624.6 μW when operating at 100-Hz sampling frequency and 1.8-V dc power supply.

Lensless CCD-based fluorometer using a micromachined optical Söller collimator

In this paper, we describe a simple charge-coupled device (CCD) based lensless fluorometer with sensitivity in the range of current ELISA plate readers. In our lensfree fluorometer, a multi-wavelength LED light source was used for fluorophore excitation. To collimate the light, we developed a simple optical Söller collimator based on a "stack of pinholes" (a stack of black PMMA with array of pinholes machined with laser) enabling the light to be collimated from the LED through the filters and the assay's microfluidics directly onto the CCD without a lens. The elimination of the lens that is used in almost all other current CCD based detection systems has four major advantages: (1) It simplifies the device design and fabrication while reducing cost. (2) It reduces the distance between the sample and the measuring device (without a lens the distance needed to focus the image on the CCD is reduced and the fluorometer can be more compact). (3) It couples the CCD and the detected surface by using an optical Söller Collimator which allows the use of filters for fluorescence detection. (4) It also uncouples the CCD and the microfluidics to enable the use of interchangeable fluidics while protecting the delicate CCD. The lensless CCD-based fluorometer is capable of detecting 16 samples simultaneously, and was used for in vitro detection of botulinum neurotoxin serotype A (BoNT-A) activity with a FRET assay that measures cleavage of a fluorophore-tagged peptide substrate specific for BoNT-A (SNAP-25) by the toxin light chain (LcA). The limit of detection (LOD) of our lensless fluorometer is 1.25 nM, which is similar to the LOD of a modern ELISA plate reader. Combined with microfluidics, this simple low cost point-of-care (POC) medical diagnostic system may be useful for the performance of many other complex medical diagnostic assays without a laboratory and thus potentially enhancing the accessibility and the quality of health care delivery in underserved populations.

Microbead-based immunoassay for simultaneous detection of Shiga toxins and isolation of Escherichia coli O157 in foods

Shiga toxin-producing Escherichia coli (STEC) is a significant foodborne pathogen with great economic consequences. There has been an increased food safety concern with this organism since outbreaks of human illnesses caused by this pathogen were first reported in 1982. Therefore, developing a reliable, sensitive, and rapid assay capable of detecting E. coli O157 and the main toxins produced by STEC (i.e., Shiga toxins 1 [Stx(1)] and 2 [Stx(2)]) will directly benefit regulatory agencies by minimizing analysis time. Here, we use Luminex technology to detect multiple analytes in a single 50-ml sample. Using commercially available monoclonal antibodies coupled to carboxylated magnetic microbeads, we developed an immunoassay capable of simultaneously serotyping E. coli O157 and detecting Stx(1) and/or Stx(2). The specificity and sensitivity of this immunoassay was tested against a collection of 34 E. coli isolates belonging to various O serogroups phenotypically different for Stx. The results were compared with microplate sandwich enzyme-linked immunosorbent assay (ELISA), and no cross-reactivity was observed for any of the monoclonal antibodies used. An increased sensitivity up to 1,000 times was observed in the microbead-based immunoassay when compared with the microplate sandwich ELISA. The results indicate that Luminex technology has the potential to simultaneously detect multiple targets without loss of specificity and/or sensitivity. A blind experiment was conducted with 48 samples of ground beef, lettuce, and milk spiked with ≤2 CFU/g E. coli. All the samples were correctly identified, with no false positives or false negatives. This microbead-based immunoassay could be extended to simultaneously detect additional foodborne pathogens and their toxic markers.

Quantum dot-based array for sensitive detection of Escherichia coli

A fluorescent quantum dot-based antibody array, used in sandwich format, has been developed to detect Escherichia coli O157:H7. Numerous parameters such as solid support, optimal concentration of immunoreagents, blocking reagents, and assay time were optimized for array construction. Quantum dot-conjugated anti-IgG was used as the detecting system. The array allows the detection of E. coli O157:H7 at concentrations below 10 CFU mL(-1) without sample enrichment, exhibiting an increase of three orders of magnitude in the limit of detection compared to ELISA. The interference caused by Gram (+) and Gram (-) bacteria was negligible at low concentrations of bacteria.