Point-of-care biosensor systems for cancer diagnostics/prognostics

Liquid Metal Ink Enabled Rapid Prototyping of Electrochemical Sensor for Wireless Glucose Detection on the Platform of Mobile Phone

Pervasive detection of blood glucose is rather critical for the real-time disease diagnosis which would provide valuable guidance for treatment planning. Here, we established a health care platform for this purpose through incorporating the glucose detection with liquid metal printed sensor and the smart phone monitoring system together. The liquid metal ink composed of bismuth indium stannic (BIS) alloy was identified as an appropriate sensor material to be quickly written or printed on polyvinyl chloride (PVC) substrate at around 59 °C to form desired electrodes. It thus eliminated the complicated procedures as usually required in conventional sensor fabrication strategies. The alloy electrodes were characterized via cyclic voltammetry to demonstrate their practical functionality. Further, unlike using the commonly adopted glucometer, a smart phone was developed as the data acquisition and display center to help improve the portability and ubiquitous virtue of the detection system. Glucose solution in different concentrations was assayed via this platform. It was shown that there is a good linear relationship between the concentration and the integral value of the curve recorded by the mobile phone, which confirms the feasibility of the present method. This quantitative point-of-care system has pervasive feature and is expected to be very useful for future low-cost electrochemical detection.

Affinity biosensors for tumor-marker analysis

The use of cancer biomarkers is emerging as one of the most promising strategies for early detection and management of cancer. Biosensors can provide advanced platforms for biomarker analysis with the advantages of being easy to use, inexpensive, rapid and offering multi-analyte testing capability. The intention of this article is to discuss recent advances and trends in affinity biosensors for cancer diagnosis, prognosis and even theragnosis. The different types of affinity biosensors will be reviewed in terms of molecular recognition element. Current challenges and trends for this technology will be also discussed, with a particular emphasis on recent developments in miRNA detection.

Optimization of amine-rich multilayer thin films for the capture and quantification of prostate-specific antigen

It is demonstrated that poly(allylamine hydrochloride)/poly(styrenesulfonate) (PAH/SPS) multilayer films can be successfully tailored for the capture and detection of small biomolecules in dilute concentrations. Based on in vitro results, these films could be potentially applied for rapid and high-throughput diagnosis of dilute biomarkers in serum or tissue. PAH presents functional amino groups that can be further reacted with desired chemistries in order to create customizable and specific surfaces for biomolecule capture. A variety of film assembly characteristics were tested (pH, molecular weight of PAH, and ionic strength) to tune the biotinylation and swelling behavior of these films to maximize detection capabilities. The resultant optimized biotinylated PAH/SPS 9.3/9.3 system was utilized in conjunction with quantum dots (Qdots) to capture and detect a dilute biomarker for prostate cancer, prostate-specific antigen (PSA). Compared to previous work, our system presents a good sensitivity for PSA detection within the clinically relevant range of 0.4-100 ng/mL.

On the Slow Diffusion of Point-of-Care Systems in Therapeutic Drug Monitoring

Recent advancements in point-of-care (PoC) technologies show great transformative promises for personalized preventative and predictive medicine. However, fields like therapeutic drug monitoring (TDM), that first allowed for personalized treatment of patients' disease, still lag behind in the widespread application of PoC devices for monitoring of patients. Surprisingly, very few applications in commonly monitored drugs, such as anti-epileptics, are paving the way for a PoC approach to patient therapy monitoring compared to other fields like intensive care cardiac markers monitoring, glycemic controls in diabetes, or bench-top hematological parameters analysis at the local drug store. Such delay in the development of portable fast clinically effective drug monitoring devices is in our opinion due more to an inertial drag on the pervasiveness of these new devices into the clinical field than a lack of technical capability. At the same time, some very promising technologies failed in the clinical practice for inadequate understanding of the outcome parameters necessary for a relevant technological breakthrough that has superior clinical performance. We hope, by over-viewing both TDM practice and its yet unmet needs and latest advancement in micro- and nanotechnology applications to PoC clinical devices, to help bridging the two communities, the one exploiting analytical technologies and the one mastering the most advanced techniques, into translating existing and forthcoming technologies in effective devices.

A versatile microparticle-based immunoaggregation assay for macromolecular biomarker detection and quantification

The rapid, sensitive and low-cost detection of macromolecular biomarkers is critical in clinical diagnostics, environmental monitoring, research, etc. Conventional assay methods usually require bulky, expensive and designated instruments and relative long assay time. For hospitals and laboratories that lack immediate access to analytical instruments, fast and low-cost assay methods for the detection of macromolecular biomarkers are urgently needed. In this work, we developed a versatile microparticle (MP)-based immunoaggregation method for the detection and quantification of macromolecular biomarkers. Antibodies (Abs) were firstly conjugated to MP through streptavidin-biotin interaction; the addition of macromolecular biomarkers caused the aggregation of Ab-MPs, which were subsequently detected by an optical microscope or optical particle sizer. The invisible nanometer-scale macromolecular biomarkers caused detectable change of micrometer-scale particle size distributions. Goat anti-rabbit immunoglobulin and human ferritin were used as model biomarkers to demonstrate MP-based immunoaggregation assay in PBS and 10% FBS to mimic real biomarker assay in the complex medium. It was found that both the number ratio and the volume ratio of Ab-MP aggregates caused by biomarker to all particles were directly correlated to the biomarker concentration. In addition, we found that the detection range could be tuned by adjusting the Ab-MP concentration. We envision that this novel MP-based immunoaggregation assay can be combined with multiple detection methods to detect and quantify macromolecular biomarkers at the nanogram per milliliter level.

Detection of Biomarkers for Different Diseases on Biosensor Surfaces Part II

In this chapter the authors analyze the binding and dissociation kinetics (if applicable) of (1) interferon-gamma as a function of aptamer variants and inclusion of spacer, (2) GST-N protein in PBS and GST-N protein in 10-fold diluted serum to a localized surface plasmon resonance coupled fluorescence biosensor, (3) cytochrome c mutant to a superoxide biosensor, (4) Carbonic Anhydrase-II to an 4-(2-aminoethyl)-benzene sulfonamide ligand on an surface plasmon resonance biosensor surface, (5) glycerol secretion from differentiated (murine 3T3-L1) adipocytes to a microfluidic platform for fluorescence-based assay, and (6) different concentrations of C-reactive protein in solution to a sandwich-type assay using reflectometric interference spectroscopy (label-free detection method).

Isolation of circulating tumour cells by physical means in a microfluidic device: a review

Isolation and enumeration of circulating tumour cells (CTCs) from human blood has a huge significance in diagnosis and prognosis of cancer.

Application of electrochemical biosensors in clinical diagnosis

Analyses in the clinical area need quick and reliable analytical methods and devices. For this purpose, biosensors can be a suitable option, whereas they are constructed to be simple for use, specific for the target analyte, capable of continuous monitoring and giving quick results, potentially low-costing and portable. In this article, we describe electrochemical biosensors developed for clinical diagnosis, namely for glucose, lactate, cholesterol, urea, creatinine, DNA, antigens, antibodies, and cancer markers assays. Chosen biosensors showed desirable sensitivity, selectivity, and potential for application on real samples. They are often designed to avoid interference with undesired components present in the monitored systems.

DNA molecular beacon-based plastic biochip: a versatile and sensitive scanometric detection platform

In this paper, we report a novel DNA molecular beacon (MB)-based plastic biochip platform for scanometric detection of a range of analytical targets. Hairpin DNA strands, which are dually modified with amino and biotin groups at their two ends are immobilized on a disposable plastic (polycarbonate) substrate as recognition element and gold nanoparticle-assisted silver-staining as signal reading protocol. Initially, the immobilized DNA probes are in their folded forms; upon target binding the hairpin secondary structure of the probe strand is "forced" open (i.e., converted to the unfolded state). Nanogold-streptavidin conjugates can then bind the terminal biotin groups and promote the deposition of rather large silver particles which can be either directly visualized or quantified with a standard flatbed scanner. We demonstrate that with properly designed probe sequences and optimized preparation conditions, a range of molecular targets, such as DNA strands, proteins (thrombin) and heavy metal ions (Hg(2+)), can be detected with high sensitivity and excellent selectivity. The detection can be done in both standard physiological buffers and real world samples. This constitutes a platform technology for performing rapid, sensitive, cost-effective, and point-of-care (POC) chemical analysis and medical diagnosis.

A multiplexable, microfluidic platform for the rapid quantitation of a biomarker panel for early ovarian cancer detection at the point-of-care

Point-of-care (POC) diagnostic platforms have the potential to enable low-cost, large-scale screening. As no single biomarker is shed by all ovarian cancers, multiplexed biomarker panels promise improved sensitivity and specificity to address the unmet need for early detection of ovarian cancer. We have configured the programmable bio-nano-chip (p-BNC)-a multiplexable, microfluidic, modular platform-to quantify a novel multi-marker panel comprising CA125, HE4, MMP-7, and CA72-4. The p-BNC is a bead-based immunoanalyzer system with a credit-card-sized footprint that integrates automated sample metering, bubble and debris removal, reagent storage and waste disposal, permitting POC analysis. Multiplexed p-BNC immunoassays demonstrated high specificity, low cross-reactivity, low limits of detection suitable for early detection, and a short analysis time of 43 minutes. Day-to-day variability, a critical factor for longitudinally monitoring biomarkers, ranged between 5.4% and 10.5%, well below the biologic variation for all four markers. Biomarker concentrations for 31 late-stage sera correlated well (R(2) = 0.71 to 0.93 for various biomarkers) with values obtained on the Luminex platform. In a 31 patient cohort encompassing early- and late-stage ovarian cancers along with benign and healthy controls, the multiplexed p-BNC panel was able to distinguish cases from controls with 68.7% sensitivity at 80% specificity. Utility for longitudinal biomarker monitoring was demonstrated with prediagnostic plasma from 2 cases and 4 controls. Taken together, the p-BNC shows strong promise as a diagnostic tool for large-scale screening that takes advantage of faster results and lower costs while leveraging possible improvement in sensitivity and specificity from biomarker panels.

Lensfree optofluidic plasmonic sensor for real-time and label-free monitoring of molecular binding events over a wide field-of-view

We demonstrate a high-throughput biosensing device that utilizes microfluidics based plasmonic microarrays incorporated with dual-color on-chip imaging toward real-time and label-free monitoring of biomolecular interactions over a wide field-of-view of >20 mm(2). Weighing 40 grams with 8.8 cm in height, this biosensor utilizes an opto-electronic imager chip to record the diffraction patterns of plasmonic nanoapertures embedded within microfluidic channels, enabling real-time analyte exchange. This plasmonic chip is simultaneously illuminated by two different light-emitting-diodes that are spectrally located at the right and left sides of the plasmonic resonance mode, yielding two different diffraction patterns for each nanoaperture array. Refractive index changes of the medium surrounding the near-field of the nanostructures, e.g., due to molecular binding events, induce a frequency shift in the plasmonic modes of the nanoaperture array, causing a signal enhancement in one of the diffraction patterns while suppressing the other. Based on ratiometric analysis of these diffraction images acquired at the detector-array, we demonstrate the proof-of-concept of this biosensor by monitoring in real-time biomolecular interactions of protein A/G with immunoglobulin G (IgG) antibody. For high-throughput on-chip fabrication of these biosensors, we also introduce a deep ultra-violet lithography technique to simultaneously pattern thousands of plasmonic arrays in a cost-effective manner.

Recent advances in bioprinting and applications for biosensing

Future biosensing applications will require high performance, including real-time monitoring of physiological events, incorporation of biosensors into feedback-based devices, detection of toxins, and advanced diagnostics. Such functionality will necessitate biosensors with increased sensitivity, specificity, and throughput, as well as the ability to simultaneously detect multiple analytes. While these demands have yet to be fully realized, recent advances in biofabrication may allow sensors to achieve the high spatial sensitivity required, and bring us closer to achieving devices with these capabilities. To this end, we review recent advances in biofabrication techniques that may enable cutting-edge biosensors. In particular, we focus on bioprinting techniques (e.g., microcontact printing, inkjet printing, and laser direct-write) that may prove pivotal to biosensor fabrication and scaling. Recent biosensors have employed these fabrication techniques with success, and further development may enable higher performance, including multiplexing multiple analytes or cell types within a single biosensor. We also review recent advances in 3D bioprinting, and explore their potential to create biosensors with live cells encapsulated in 3D microenvironments. Such advances in biofabrication will expand biosensor utility and availability, with impact realized in many interdisciplinary fields, as well as in the clinic.

Toward integrated molecular diagnostic system (i MDx): principles and applications

Integrated molecular diagnostic systems ( iMDx), which are automated, sensitive, specific, user-friendly, robust, rapid, easy-to-use, and portable, can revolutionize future medicine. This review will first focus on the components of sample extraction, preservation, and filtration necessary for all point-of-care devices to include for practical use. Subsequently, we will look for low-powered and precise methods for both sample amplification and signal transduction, going in-depth to the details behind their principles. The final field of total device integration and its application to the clinical field will also be addressed to discuss the practicality for future patient care. We envision that microfluidic systems hold the potential to breakthrough the number of problems brought into the field of medical diagnosis today.

Selective detection of target proteins by peptide-enabled graphene biosensor

Direct molecular detection of biomarkers is a promising approach for diagnosis and monitoring of numerous diseases, as well as a cornerstone of modern molecular medicine and drug discovery. Currently, clinical applications of biomarkers are limited by the sensitivity, complexity and low selectivity of available indirect detection methods. Electronic 1D and 2D nano-materials such as carbon nanotubes and graphene, respectively, offer unique advantages as sensing substrates for simple, fast and ultrasensitive detection of biomolecular binding. Versatile methods, however, have yet to be developed for simultaneous functionalization and passivation of the sensor surface to allow for enhanced detection and selectivity of the device. Herein, we demonstrate selective detection of a model protein against a background of serum protein using a graphene sensor functionalized via self-assembling multifunctional short peptides. The two peptides are engineered to bind to graphene and undergo co-assembly in the form of an ordered monomolecular film on the substrate. While the probe peptide displays the bioactive molecule, the passivating peptide prevents non-specific protein adsorption onto the device surface, ensuring target selectivity. In particular, we demonstrate a graphene field effect transistor (gFET) biosensor which can detect streptavidin against a background of serum bovine albumin at less than 50 ng/ml. Our nano-sensor design, allows us to restore the graphene surface and utilize each sensor in multiple experiments. The peptide-enabled gFET device has great potential to address a variety of bio-sensing problems, such as studying ligand-receptor interactions, or detection of biomarkers in a clinical setting.

Biosensors for the detection of circulating tumour cells

Metastasis is the cause of most cancer deaths. Circulating tumour cells (CTCs) are cells released from the primary tumour into the bloodstream that are considered the main promoters of metastasis. Therefore, these cells are targets for understanding tumour biology and improving clinical management of the disease. Several techniques have emerged in recent years to isolate, detect, and characterise CTCs. As CTCs are a rare event, their study requires multidisciplinary considerations of both biological and physical properties. In addition, as isolation of viable cells may give further insights into metastatic development, cell recovery must be done with minimal cell damage. The ideal system for CTCs analysis must include maximum efficiency of detection in real time. In this sense, new approaches used to enrich CTCs from clinical samples have provided an important improvement in cell recovery. However, this progress should be accompanied by more efficient strategies of cell quantification. A range of biosensor platforms are being introduced into the technology for CTCs quantification with promising results. This review provides an update on recent progress in CTCs identification using different approaches based on sensor signaling.

Construction and validation of a Sambucus nigra biosensor for cancer-associated STn antigen

A label-free electrochemical impedance spectroscopy biosensor for selective detection and discrimination of the cancer-associated sialyl-Tn (STn) antigen was developed by using Sambucus nigra agglutinin type I (SNA-I) as the recognition element. The SNA-I biosensor was constructed by immobilizing the lectin on screen-printed gold electrodes. The formation of a complex between SNA-I and STn-containing glycoproteins (transferrin and bovine submaxillary mucin) was monitored by measuring the impedance increase of the biosensor. The increase in electron transfer resistance was linearly proportional to the concentration of the glycoproteins up to 70 ng of transferrin and 40 ng of bovine submaxillary mucin, with a limit of detection of 20 ng for transferrin. Albumin, the most abundant serum protein, did not interfere in the detection of the STn-glycoproteins up to a concentration of 0.2 mg ml(-1). The developed lectin-based biosensor was used to evaluate the STn-expression in serum samples and discriminate samples from healthy individuals and patients with different types of malignant tumors, mostly carcinomas, where the increased expression of STn aberrant glycans is well established. This work demonstrates the feasibility of employing SNA-I to selectively recognize the STn epitope in glycoproteins and the use of the constructed biosensor was effective in the analysis of serum samples with the ability to discriminate in a fast way between cancer and healthy status. The proposed biosensor could be used for high-throughput, label-free profiling of the cancer-associated STn glycan expression in serum for diagnosis and therapy monitoring.

Dip biosensor based on localized surface plasmon resonance at the tip of an optical fiber

A dip biosensor is realized by depositing metallic nanoparticles onto the tip of a cleaved optical fiber. Light coupled into the fiber interacts with the localized surface plasmons within the nanoparticles at the tip; a portion of the scattered light recouples into the optical fiber and is analyzed by a spectrometer. Characterization of the sensor demonstrates an inverse relationship between the sensitivity and the number of particles deposited onto the surface, with smaller quantities leading to greater sensitivity. The results obtained showed also that by depositing nanoparticles with distinct localized surface plasmon resonance signatures with limited overlap, as for the case of gold and silver nanospheres, a multiplexed dip biosensor can be realized by simply functionalizing the different nanoparticles with different antibodies after the fashion of an immunoassay. In this way different localized surface plasmons resonance bands responsive to different target analytes can be separately monitored, as further presented below, requiring a minimal quantity of reagents both for the functionalization process and for the sample analysis.

Shadow masking for nanomaterial-based biosensors incorporated with a microfluidic device

Integrating PDMS channels and chips containing pre-functionalized biosensors into microfluidic devices with irreversible sealing has been challenging because the integration process requires use of an O2 plasma treatment that usually destroys the biosensors. In this study, we examined the usefulness of introducing a shadow mask into the process as a method of protecting the pre-functionalized biosensors. Single nanowire sensors were pre-functionalized with fluorescently labeled biomolecules and then subjected to O2 plasma with and without the shadow mask. Results from the two groups were then compared. Those sensors without a shadow mask were destroyed, giving the sensor an infinite resistance and reduced fluorescence intensity. In contrast, the sensors with the shadow mask were protected and exhibited little changes in the resistance and fluorescence intensity. Then two different nanowires, aptamers incorporated polypyrrole nanowire (entrapment) and antibodies immobilized polyaniline nanowire (surface covalent binding), were used to investigate their detection performance before and after the plasma treatment in the presence of shadow mask. The protected samples showed a good sensitivity to the targets with a slight reduction in response compared with the as-prepared samples. After the O2 plasma treatment, the microfluidic channels were integrated with single nanowire biosensors. This microfluidic biosensor showed a high sensitivity with about ~0.5 % change in conductance at the lowest IgE protein concentration of 10 pM.

Smart-phone based computational microscopy using multi-frame contact imaging on a fiber-optic array

We demonstrate a cellphone based contact microscopy platform, termed Contact Scope, which can image highly dense or connected samples in transmission mode. Weighing approximately 76 grams, this portable and compact microscope is installed on the existing camera unit of a cellphone using an opto-mechanical add-on, where planar samples of interest are placed in contact with the top facet of a tapered fiber-optic array. This glass-based tapered fiber array has ~9 fold higher density of fiber optic cables on its top facet compared to the bottom one and is illuminated by an incoherent light source, e.g., a simple light-emitting-diode (LED). The transmitted light pattern through the object is then sampled by this array of fiber optic cables, delivering a transmission image of the sample onto the other side of the taper, with ~3× magnification in each direction. This magnified image of the object, located at the bottom facet of the fiber array, is then projected onto the CMOS image sensor of the cellphone using two lenses. While keeping the sample and the cellphone camera at a fixed position, the fiber-optic array is then manually rotated with discrete angular increments of e.g., 1-2 degrees. At each angular position of the fiber-optic array, contact images are captured using the cellphone camera, creating a sequence of transmission images for the same sample. These multi-frame images are digitally fused together based on a shift-and-add algorithm through a custom-developed Android application running on the smart-phone, providing the final microscopic image of the sample, visualized through the screen of the phone. This final computation step improves the resolution and also removes spatial artefacts that arise due to non-uniform sampling of the transmission intensity at the fiber optic array surface. We validated the performance of this cellphone based Contact Scope by imaging resolution test charts and blood smears.

Recent advances in cortisol sensing technologies for point-of-care application

Everyday lifestyle related issues are the main cause of psychological stress, which contributes to health disparities experienced by individuals. Prolonged exposure to stress leads to the activation of signaling pathways from the brain that leads to release of cortisol from the adrenal cortex. Various biomarkers have been affected by psychological stress, but cortisol "a steroid hormone" is known as a potential biomarker for its estimation. Cortisol can also be used as a target analyte marker to determine the effect of exposure such as organophosphates on central nervous system, which alters the endocrine system, leading to imbalance in cortisol secretion. Cortisol secretion of individuals depends on day-night cycle and field environment hence its detection at point-of-care (POC) is deemed essential to provide personalized healthcare. Chromatographic techniques have been traditionally used to detect cortisol. The issues relating to assay formation, system complexity, and multistep extraction/purification limits its application in the field. In order to overcome these issues and to make portable and effective miniaturized platform, various immunoassays sensing strategies are being explored. However, electrochemical immunosensing of cortisol is considered as a recent advancement towards POC application. Highly sensitive, label-free and selective cortisol immunosensor based on microelectrodes are being integrated with the microfluidic system for automated diurnal cortisol monitoring useful for personalized healthcare. Although the reported sensing devices for cortisol detection may have a great scope to improve portability, electronic designing, performance of the integrated sensor, data safety and lifetime for point-of-care applications, This review is an attempt to describe the various cortisol sensing platforms and their potential to be integrated into a wearable system for online and continuous monitoring of cortisol rhythm at POC as a function of one's environment.

On-line protein capture on magnetic beads for ultrasensitive microfluidic immunoassays of cancer biomarkers

Accurate, sensitive, multiplexed detection of biomarker proteins holds significant promise for personalized cancer diagnostics. Here we describe the incorporation of a novel on-line chamber to capture cancer biomarker proteins on magnetic beads derivatized with 300,000 enzyme labels and 40,000 antibodies into a modular microfluidic immunoarray. Capture and detection chambers are produced from PDMS on machined molds and do not require lithography. Protein analytes are captured from serum or other biological samples in the stirred capture chamber on the beads held in place magnetically. The beads are subsequently washed free of sample components, and wash solutions sent to waste. Removal of the magnet and valve switching sends the magnetic bead-protein bioconjugates into a detection chamber where they are captured on 8 antibody-decorated gold nanoparticle-film sensors and detected amperometrically. Most steps in the immunoassay including protein capture, washing and measurement are incorporated into the device. In simultaneous assays, the microfluidic system gave ultralow detection limits of 5 fg mL(-1) for interleukin-6 (IL-6) and 7 fg mL(-1) for IL-8 in serum. Accuracy was demonstrated by measuring IL-6 and IL-8 in conditioned media from oral cancer cell lines and showing good correlations with standard ELISAs. The on-line capture chamber facilitates rapid, sensitive, repetitive protein separation and measurement in 30 min in a semi-automated system adaptable to multiplexed protein detection.

Detection of IP-10 protein marker in undiluted blood serum via an electrochemical E-DNA scaffold sensor

We describe an electrochemical analog of fluorescence polarization that supports the quantitative measurement of a specific protein, the chemokine IP-10, directly in undiluted blood serum. The sensor is label-free, wash-free, and electronic, suggesting it could support point-of-care detection of diagnostic proteins in largely unprocessed clinical samples.

Dielectrophoresis: applications and future outlook in point of care

Dielectrophoresis (DEP) is a label free, noninvasive, stand alone, rapid, and sensitive particle manipulation and characterization technique. Improvements in micro-electro-mechanical systems technology have enabled the biomedical applications of DEP over the past decades. By this way, integration of DEP into lab-on-a-chip systems has become achievable, creating a potential tool for point-of-care (POC) systems. DEP can be utilized in many different POC applications including early detection and prognosis of various cancer types, diagnosis of infectious diseases, blood cell analysis, and stem cell therapy. However, there are still some challenges to be resolved to have DEP-based devices available in POC market. Today, researchers have focused on these challenges to have this powerful theory as a solution for many POC applications. Here, DEP theory, cell modeling, and most common device structures are introduced briefly. Next, POC applications of DEP theory, such as cell (blood, cancer, stem, and fetal) and microorganism separation, manipulation, and enrichment for diagnosis and prognosis, are explained. Integration of DEP with other detection techniques to have more sensitive systems is summarized. Finally, future outlook for DEP-based systems are discussed with some challenges, which are currently preventing these systems to be a common tool for POC applications, and possible solutions.

Vertical flow immunoassay (VFA) biosensor for a rapid one-step immunoassay

A highly rapid, one-step immunoassay of high sensitivity C-reactive protein (hsCRP) using a biosensor with a vertical flow immunoassay (VFA) was developed. The VFA biosensor was primarily composed of a sample pad, conjugate pad, FTH film and nitrocellulose (NC) membrane, which were all vertically stacked upon one another. Anti-hsCRP and secondary antibodies were consecutively immobilized on the NC membrane at the position below the holes. Gold nanoparticles (AuNPs) conjugated with another anti-hsCRP antibody were encapsulated in the conjugation pad. Various assay conditions, including the size of the hole and the sample volume, were optimized. Under optimized conditions, hsCRP concentrations from 0.01 to 10 μg mL(-1) were detected within 2 min. In comparison with a lateral flow assay (LFA) system, the VFA sensor showed a gradual increase of signal in a concentration-dependent manner without a hook effect in the tested range.

Label-free biosensor based on an electrical tracing-assisted silicon microring resonator with a low-cost broadband source

We present a novel biosensor based on an electrical tracing-assisted silicon dual-microring resonator sensor system. The dual-microring system comprises one microring resonator as a sensing element and the other microring resonator integrated with an electrical controller as a tracing element. The resonance wavelength shift of the sensing microring induced by the refractive index change due to antigen-ligand bindings is traced and determined by direct voltage applied to the electrical tunable tracing microring. The sensor system enables the use of a low-cost broadband light source instead of a bulky and expensive tunable laser, which allows the development of cost-effective point-of-care diagnostic devices by significantly reducing the device cost and increasing its portability. The sensing capability of the developed dual-microring sensor was investigated using biotin-streptavidin binding as a model system. We have demonstrated the quantitative detection of streptavidin over a broad range of concentrations down to 190 pM by monitoring the electrical power applied to the tracing ring. We have also validated the sensing principle of the dual-microring system by a direct comparison between the calculated and measured values for the resonance wavelength shift of the sensing microring. Furthermore, we have shown the quantitative and specific detection of a well-known breast cancer biomarker, human epidermal growth factor receptor 2 (HER2), in a bovine serum albumin solution using the antibody-modified dual-microring sensor system.

Reading disc-based bioassays with standard computer drives

Traditional methods of disease diagnosis are both time-consuming and labor-intensive, and many tests require expensive instrumentation and trained professionals, which restricts their use to biomedical laboratories. Because patients can wait several days (even weeks) for the results, the consequences of delayed treatment could be disastrous. Therefore, affordable and simple point-of-care (POC) biosensor devices could fill a diagnostic niche in the clinic or even at home, as personal glucose meters do for diabetics. These devices would allow patients to check their own health conditions and enable physicians to make prompt treatment decisions, which could improve the chances for rapid recovery and cure. Compact discs (CDs) provide inexpensive substrate materials for the preparation of microarray biochips, and conventional computer drives/disc players can be adapted as precise optical reading devices for signal processing. Researchers can employ the polycarbonate (PC) base of a CD as an alternative substrate to glass slides or silicon wafers for the preparation of microanalytical devices. Using the characteristic optical phenomena occurring on the metal layer of a CD, researchers can develop biosensors based on advanced spectroscopic readout (interferometry or surface plasmon resonance). If researchers integrate microfluidic functions with CD mechanics, they can control fluid transfer through the spinning motion of the disc, leading to "lab-on-a-CD" devices. Over the last decade, our laboratory has focused on the construction of POC biosensor devices from off-the-shelf CDs or DVDs and standard computer drives. Besides the initial studies of the suitability of CDs for surface and materials chemistry research (fabrication of self-assembled monolayers and oxide nanostructures), we have demonstrated that an ordinary optical drive, without modification of either the hardware or the software driver, can function as the signal transducing element for reading disc-based bioassays quantitatively. In this Account, we first provide a brief introduction to CD-related materials chemistry and microfluidics research. Then we describe the mild chemistry developed in our laboratory for the preparation of computer-readable biomolecular screening assays: photochemical activation of the polycarbonate (PC) disc surface and immobilization and delivery of probe and target biomolecules. We thoroughly discuss the analysis of the molecular recognition events: researchers can "read" these devices quantitatively with an unmodified optical drive of any personal computer. Finally, and critically, we illustrate our digitized molecular diagnosis approach with three trial systems: DNA hybridization, antibody-antigen binding, and ultrasensitive lead detection with a DNAzyme assay. These examples demonstrate the broad potential of this new analytical/diagnostic tool for medical screening, on-site food/water safety testing, and remote environmental monitoring.

Dual-responsive gold nanoparticles for colorimetric recognition and testing of carbohydrates with a dispersion-dominated chromogenic process

A dispersion-dominated colorimetric approach for the recognition of carbohydrates based on biomolecule-responsive AuNPs is presented. Taking advantage of the unique dual-responsiveness of smart copolymers, the aggregation and dispersion of AuNPs can be modulated by both temperature and different kinds of carbohydrates, giving rise to a novel chromogenic mechanism for the recognition and testing of carbohydrates in aqueous media.

Optical imaging techniques for point-of-care diagnostics

Improving access to effective and affordable healthcare has long been a global endeavor. In this quest, the development of cost-effective and easy-to-use medical testing equipment that enables rapid and accurate diagnosis is essential to reduce the time and costs associated with healthcare services. To this end, point-of-care (POC) diagnostics plays a crucial role in healthcare delivery in both developed and developing countries by bringing medical testing to patients, or to sites near patients. As the diagnosis of a wide range of diseases, including various types of cancers and many endemics, relies on optical techniques, numerous compact and cost-effective optical imaging platforms have been developed in recent years for use at the POC. Here, we review the state-of-the-art optical imaging techniques that can have a significant impact on global health by facilitating effective and affordable POC diagnostics.

Electroanalysis of single-nucleotide polymorphism by hairpin DNA architectures

Genetic analysis of infectious and genetic diseases and cancer diagnostics require the development of efficient tools for fast and reliable analysis of single-nucleotide polymorphism (SNP) in targeted DNA and RNA sequences often responsible for signalling disease onset. Here, we highlight the main trends in the development of electrochemical genosensors for sensitive and selective detection of SNP that are based on hairpin DNA architectures exhibiting better SNP recognition properties compared with linear DNA probes. SNP detection by electrochemical hairpin DNA beacons is discussed, and comparative analysis of the existing SNP sensing strategies based on enzymatic and nanoparticle signal amplification schemes is presented.

Porous bead-based diagnostic platforms: bridging the gaps in healthcare

Advances in lab-on-a-chip systems have strong potential for multiplexed detection of a wide range of analytes with reduced sample and reagent volume; lower costs and shorter analysis times. The completion of high-fidelity multiplexed and multiclass assays remains a challenge for the medical microdevice field; as it struggles to achieve and expand upon at the point-of-care the quality of results that are achieved now routinely in remote laboratory settings. This review article serves to explore for the first time the key intersection of multiplexed bead-based detection systems with integrated microfluidic structures alongside porous capture elements together with biomarker validation studies. These strategically important elements are evaluated here in the context of platform generation as suitable for near-patient testing. Essential issues related to the scalability of these modular sensor ensembles are explored as are attempts to move such multiplexed and multiclass platforms into large-scale clinical trials. Recent efforts in these bead sensors have shown advantages over planar microarrays in terms of their capacity to generate multiplexed test results with shorter analysis times. Through high surface-to-volume ratios and encoding capabilities; porous bead-based ensembles; when combined with microfluidic elements; allow for high-throughput testing for enzymatic assays; general chemistries; protein; antibody and oligonucleotide applications.

Bio-mimetically synthesized Ag@BSA microspheres as a novel electrochemical biosensing interface for sensitive detection of tumor cells

The use of a novel cytosensor, comprised of bio-mimetically synthesized Ag@BSA composite microspheres, for the detection of KB cells (a model system) is described. The Ag@BSA composite microspheres were immobilized on Au electrodes via Au-thiol bonds. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) images revealed that the Ag@BSA were well-dispersed microspheres with an average diameter of 500 nm, including the monolayer of BSA. The immobilization of Ag@BSA composite microspheres onto Au electrodes is thought to increase the electrode surface area and accelerate the electron transfer rate while providing a highly stable matrix for the convenient conjugation of target molecules (such as folic acid) and the prolonged incubation of cells. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies showed that the fabricated cytosensor was able to detect KB cells ranging from 6.0×10(1) to 1.2×10(8) cells mL(-1) with a lower detection limit of 20 cells mL(-1). Due to its facile synthesis, high stability and reproducibility and cytocompatibility, the novel cytosensor described here could find multifarious uses in applications, such as cancer diagnosis, drug screening and cell adhesion studies.