On-chip micro-biosensor for the detection of human CD4+ cells based on AC impedance and optical analysis

Artificial Intelligence in Point-of-Care Biosensing: Challenges and Opportunities

The integration of artificial intelligence (AI) into point-of-care (POC) biosensing has the potential to revolutionize diagnostic methodologies by offering rapid, accurate, and accessible health assessment directly at the patient level. This review paper explores the transformative impact of AI technologies on POC biosensing, emphasizing recent computational advancements, ongoing challenges, and future prospects in the field. We provide an overview of core biosensing technologies and their use at the POC, highlighting ongoing issues and challenges that may be solved with AI. We follow with an overview of AI methodologies that can be applied to biosensing, including machine learning algorithms, neural networks, and data processing frameworks that facilitate real-time analytical decision-making. We explore the applications of AI at each stage of the biosensor development process, highlighting the diverse opportunities beyond simple data analysis procedures. We include a thorough analysis of outstanding challenges in the field of AI-assisted biosensing, focusing on the technical and ethical challenges regarding the widespread adoption of these technologies, such as data security, algorithmic bias, and regulatory compliance. Through this review, we aim to emphasize the role of AI in advancing POC biosensing and inform researchers, clinicians, and policymakers about the potential of these technologies in reshaping global healthcare landscapes.

A Review on Microfluidics-Based Impedance Biosensors

Electrical impedance biosensors are powerful and continuously being developed for various biological sensing applications. In this line, the sensitivity of impedance biosensors embedded with microfluidic technologies, such as sheath flow focusing, dielectrophoretic focusing, and interdigitated electrode arrays, can still be greatly improved. In particular, reagent consumption reduction and analysis time-shortening features can highly increase the analytical capabilities of such biosensors. Moreover, the reliability and efficiency of analyses are benefited by microfluidics-enabled automation. Through the use of mature microfluidic technology, complicated biological processes can be shrunk and integrated into a single microfluidic system (e.g., lab-on-a-chip or micro-total analysis systems). By incorporating electrical impedance biosensors, hand-held and bench-top microfluidic systems can be easily developed and operated by personnel without professional training. Furthermore, the impedance spectrum provides broad information regarding cell size, membrane capacitance, cytoplasmic conductivity, and cytoplasmic permittivity without the need for fluorescent labeling, magnetic modifications, or other cellular treatments. In this review article, a comprehensive summary of microfluidics-based impedance biosensors is presented. The structure of this article is based on the different substrate material categorizations. Moreover, the development trend of microfluidics-based impedance biosensors is discussed, along with difficulties and challenges that may be encountered in the future.

Biosensors for Detecting Lymphocytes and Immunoglobulins

Lymphocytes (B, T and natural killer cells) and immunoglobulins are essential for the adaptive immune response against external pathogens. Flow cytometry and enzyme-linked immunosorbent (ELISA) kits are the gold standards to detect immunoglobulins, B cells and T cells, whereas the impedance measurement is the most used technique for natural killer cells. For point-of-care, fast and low-cost devices, biosensors could be suitable for the reliable, stable and reproducible detection of immunoglobulins and lymphocytes. In the literature, such biosensors are commonly fabricated using antibodies, aptamers, proteins and nanomaterials, whereas electrochemical, optical and piezoelectric techniques are used for detection. This review describes how these measurement techniques and transducers can be used to fabricate biosensors for detecting lymphocytes and the total content of immunoglobulins. The various methods and configurations are reported, along with the advantages and current limitations.

Ultrasensitive detection of pathogenic viruses with electrochemical biosensor: State of the art

Last few decades, viruses are a real menace to human safety. Therefore, the rapid identification of viruses should be one of the best ways to prevent an outbreak and important implications for medical healthcare. The recent outbreak of coronavirus disease (COVID-19) is an infectious disease caused by a newly discovered coronavirus which belongs to the single-stranded, positive-strand RNA viruses. The pandemic dimension spread of COVID-19 poses a severe threat to the health and lives of seven billion people worldwide. There is a growing urgency worldwide to establish a point-of-care device for the rapid detection of COVID-19 to prevent subsequent secondary spread. Therefore, the need for sensitive, selective, and rapid diagnostic devices plays a vital role in selecting appropriate treatments and to prevent the epidemics. During the last decade, electrochemical biosensors have emerged as reliable analytical devices and represent a new promising tool for the detection of different pathogenic viruses. This review summarizes the state of the art of different virus detection with currently available electrochemical detection methods. Moreover, this review discusses different fabrication techniques, detection principles, and applications of various virus biosensors. Future research also looks at the use of electrochemical biosensors regarding a potential detection kit for the rapid identification of the COVID-19.

Continuous Label-Free Electronic Discrimination of T Cells by Activation State

The sensitivity and speed with which the immune system reacts to host disruption is unrivaled by any detection method for pathogenic biomarkers or infectious signatures. Engagement of cellular immunity in response to infections or cancer is contingent upon activation and subsequent cytotoxic activity by T cells. Thus, monitoring T cell activation can reliably serve as a metric for disease diagnosis as well as therapeutic prognosis. Rapid and direct quantification of T cell activation states, however, has been hindered by challenges associated with antigen target identification, labeling requirements, and assay duration. Here we present an electronic, label-free method for simultaneous separation and evaluation of T cell activation states. Our device utilizes a microfluidic design integrated with nanolayered electrode structures for dielectrophoresis (DEP)-driven discrimination of activated vs naïve T cells at single-cell resolution and demonstrates rapid (<2 min) separation of T cells at high single-pass efficiency as quantified by an on-chip Coulter counter module. Our device represents a microfluidic tool for electronic assessment of immune activation states and, hence, a portable diagnostic for quantitative evaluation of immunity and disease state. Further, its ability to achieve label-free enrichment of activated immune cells promises clinical utility in cell-based immunotherapies.

Cell Line Classification Using Electric Cell-Substrate Impedance Sensing (ECIS)

We present new methods for cell line classification using multivariate time series bioimpedance data obtained from electric cell-substrate impedance sensing (ECIS) technology. The ECIS technology, which monitors the attachment and spreading of mammalian cells in real time through the collection of electrical impedance data, has historically been used to study one cell line at a time. However, we show that if applied to data from multiple cell lines, ECIS can be used to classify unknown or potentially mislabeled cells, factors which have previously been associated with the reproducibility crisis in the biological literature. We assess a range of approaches to this new problem, testing different classification methods and deriving a dictionary of 29 features to characterize ECIS data. Most notably, our analysis enriches the current field by making use of simultaneous multi-frequency ECIS data, where previous studies have focused on only one frequency; using classification methods to distinguish multiple cell lines, rather than simple statistical tests that compare only two cell lines; and assessing a range of features derived from ECIS data based on their classification performance. In classification tests on fifteen mammalian cell lines, we obtain very high out-of-sample predictive accuracy. These preliminary findings provide a baseline for future large-scale studies in this field.

Impedimetric Biosensors for Detecting Vascular Endothelial Growth Factor (VEGF) Based on Poly(3,4-ethylene dioxythiophene) (PEDOT)/Gold Nanoparticle (Au NP) Composites

In advanced forms of diabetic retinopathy, retinal vascular occlusive disease and exudative age-related macular degeneration, vision loss is associated with elevated levels or extravasation of vascular endothelial-derived growth factor (VEGF) into the retina, vitreous, and anterior chamber of the eye. We hypothesize that point-of-care biosensors, capable of rapidly and precisely measuring VEGF levels within the eye will assist clinicians in assessing disease severity, and in establishing individualized dosing intervals for intraocular anti-VEGF injection therapy. An impedance biosensor based on a poly(3,4-ethylenedioxythiophene) (PEDOT)/gold nanoparticle (Au NP) composite was developed for detecting VEGF. PEDOT with Au NP was electrochemically deposited on three different medical electrode sensor designs: free-standing pads, screen printed dots, and interdigitated micro-strip electrodes. Anti-VEGF antibody was covalently immobilized on the surface of the polymer films through attachment to citrate-functionalized Au NPs, and the resulting composites were used to detect VEGF-165 by electrochemical impedance spectroscopy (EIS). The PEDOT-Au NP composite materials were characterized using optical microscopy, SEM/EDS, FIB, TEM, and STEM techniques. Among the different micro-electrodes, the interdigitated strip shape showed the best overall film stability and reproducibility. A linear relationship was established between the charge transfer resistance (R_ct) and VEGF concentration. The detection limit of VEGF was found to be 0.5 pg/mL, with a correlation coefficient of 0.99 ± 0.064%. These results indicate that the proposed PEDOT/Au NP composites can be used in designing low-cost and accurate VEGF biosensors for applications such as clinical diagnosis of VEGF-mediated eye disease.

A Single-Bead-Based, Fully Integrated Microfluidic System for High-Throughput CD4+T Lymphocyte Enumeration

A single-bead-based, fully integrated microfluidic system has been developed for high-throughput CD4+T lymphocyte enumeration at point-of-care testing. Instead of directly counting CD4+T lymphocytes, CD4+T lymphocyte enumeration is achieved by quantitatively detecting CD4 antigen from the lysed blood sample with a functionalized polycarbonate single bead based on chemiluminescence. To implement the sandwiched chemiluminescence immunoassay with reduced nonspecific binding, a streamlined microfluidic chip with multiple reaction chambers is developed to allow each reaction step to be completed in an independent chamber where reagent is pre-stored. With simple magnetic control, the single bead with an embedded ferrous core can be consecutively transported between each of two adjacent chambers for different reactions. Meanwhile, enhanced mixing can be achieved by moving the single bead back and forth inside one chamber with magnetic actuation. High-throughput detection can be performed when a linear actuation stage is adopted to introduce synchronous magnetic control to multiple single beads in parallel microfluidic chips. A sensitive charge-coupled device (CCD) camera is adopted for high-throughput chemiluminescence detection from multiple single beads. Experimental results show that with the fully integrated microfluidic system, easy-to-operate, accurate, low-cost, immediate, and high-throughput CD4+T lymphocyte enumeration can be successfully achieved at resource-poor settings.

CMOS Electrochemical Instrumentation for Biosensor Microsystems: A Review

Modern biosensors play a critical role in healthcare and have a quickly growing commercial market. Compared to traditional optical-based sensing, electrochemical biosensors are attractive due to superior performance in response time, cost, complexity and potential for miniaturization. To address the shortcomings of traditional benchtop electrochemical instruments, in recent years, many complementary metal oxide semiconductor (CMOS) instrumentation circuits have been reported for electrochemical biosensors. This paper provides a review and analysis of CMOS electrochemical instrumentation circuits. First, important concepts in electrochemical sensing are presented from an instrumentation point of view. Then, electrochemical instrumentation circuits are organized into functional classes, and reported CMOS circuits are reviewed and analyzed to illuminate design options and performance tradeoffs. Finally, recent trends and challenges toward on-CMOS sensor integration that could enable highly miniaturized electrochemical biosensor microsystems are discussed. The information in the paper can guide next generation electrochemical sensor design.

Nano-Biosensor for Monitoring the Neural Differentiation of Stem Cells

In tissue engineering and regenerative medicine, monitoring the status of stem cell differentiation is crucial to verify therapeutic efficacy and optimize treatment procedures. However, traditional methods, such as cell staining and sorting, are labor-intensive and may damage the cells. Therefore, the development of noninvasive methods to monitor the differentiation status in situ is highly desirable and can be of great benefit to stem cell-based therapies. Toward this end, nanotechnology has been applied to develop highly-sensitive biosensors to noninvasively monitor the neural differentiation of stem cells. Herein, this article reviews the development of noninvasive nano-biosensor systems to monitor the neural differentiation of stem cells, mainly focusing on optical (plasmonic) and eletrochemical methods. The findings in this review suggest that novel nano-biosensors capable of monitoring stem cell differentiation are a promising type of technology that can accelerate the development of stem cell therapies, including regenerative medicine.

Impedimetric quantification of cells encapsulated in hydrogel cultured in a paper-based microchamber

Recently, 3D cell culture technique was proposed to provide a more physiologically-meaningful environment for cell-based assays. With the development of microfluidics technology, cellular response can be quantified by impedance measurement technique in a real-time and non-invasive manner. However, handling of these microfluidic systems requires a trained engineering personnel and the operation is not compatible to traditional biological research laboratories. In this work, we incorporated the impedance measurement technique to paper-based 3D cell culture model and demonstrated non-invasive quantification of cells encapsulated in hydrogel during the culture course. A cellulose filter paper was patterned with an array of circular microchambers. Cells were encapsulated in hydrogel and loaded to the microchambers for culturing cells in 3D environment. At the preset schedule during the culture course, the paper was placed on a glass substrate with measurement electrodes for the impedance measurement. Cells in each microchamber was represented by impedance magnitude and cell proliferation could be studied over time. Also, conventional bio-assay was performed to further confirm the feasibility of the impedimetric quantification of cells encapsulated in hydrogel cultured in the paper-based microchamber. This technique provides a convenient, fast, and non-invasive approach to monitor cells cultured in 3D environment. It has potential to be developed for routine 3D cell culture protocol in biological research laboratories.

Rapid, low-cost and instrument-free CD4+ cell counting for HIV diagnostics in resource-poor settings

We present a novel, user-friendly and widely autonomous point-of-care diagnostic to enable HIV monitoring in resource-poor regions where the current pandemic is most prevalent. To specifically isolate magnetically tagged CD4+ cells directly from patient blood, the low-cost and disposable microfluidic chip operates by dual-force CD4+ cell magnetophoresis; whereby the interplay of flow and magnetic fields governs the trajectory of target cells depending on whether the cell binds to a magnetic microbead. Instrument-free pumping is implemented by a finger-actuated elastic membrane; tagged beads are laterally deflected by a small and re-useable permanent magnet. The single-depth and monolithic microfluidic structure can easily be fabricated in a single casting step. After their magnetophoretic isolation from whole blood, estimation of CD4+ cell concentrations is then measured by bright-field inspection of the capture chamber. In addition, an optional fluorescence measurement can be used for confirmation of the bright-field result if required. On-chip CD4+ estimation produces a linear response over the full range of medically relevant CD4+ cell concentrations. Our technology combines high-efficiency capture (93.0 ± 3.3%) and cell enumeration.

High-throughput impedance spectroscopy biosensor array chip

Impedance spectroscopy is a powerful tool for characterizing materials that exhibit a frequency dependent behaviour to an applied electric field. This paper introduces a fully integrated multi-channel impedance extraction circuit that can both generate AC stimulus signals over a broad frequency range and also measure and digitize the real and imaginary components of the impedance response. The circuit was fabricated in a 0.5 μm complementary metal-oxide semiconductor. Tailored for cellular membrane interface characterization, the signal generator produces sinusoidal waves from 10 mHz to 10 kHz. To suit a variety of applications, the impedance extraction circuit provides a programmable current measurement range from 100 pA to 100 nA with a measured resolution of approximately 100 fA. Occupying only 0.045 mm(2) per measurement channel, the circuit is compact enough to include nearly 200 channels in a 3×3 mm(2) die area.

Micro- and nanotechnology for HIV/AIDS diagnostics in resource-limited settings

Thirty-four million people are living with HIV worldwide, a disproportionate number of whom live in resource-limited settings. Proper clinical management of AIDS, the disease caused by HIV, requires regular monitoring of both the status of the host's immune system and levels of the virus in their blood. Therefore, more accessible technologies capable of performing a CD4+ T cell count and HIV viral load measurement in settings where HIV is most prevalent are desperately needed to enable better treatment strategies and ultimately quell the spread of the virus within populations. This review discusses micro- and nanotechnology solutions to performing these key clinical measurements in resource-limited settings.

Non-invasive measurement of cell viability in 3-dimensional cell culture construct

In this work, a non-invasive measurement technique for the quantitative determination of cell viability in a three-dimensional (3D) cell culture construct is proposed. This technique is based on on-site electrical impedance measurement. A microfluidic chip with a 3D culture chamber is fabricated to demonstrate this technique. In vitro 3D cell culture has been interpreted for faithfully representation of the in vivo cellular responses in 3D cell culture construct is normally time-consuming and labor-intensive. In this study, the microfluidic chip consists of a culture chamber, in which a pair of vertical electrodes at its opposite sidewalls was embedded, and a fluidic channel for drug perfusion. Cancer cells encapsulated in agarose gel were loaded into the culture chamber to perform 3D cell culture under the perfusion of culture medium and anti-cancer drug in different concentrations (6, 12, 18, and 24 µg/ml) for 2 days. Since higher drug concentration led to more cell damage or death, the total impedance magnitude of the culture construct was shown to be reasonably proportional to the anti-cancer drug concentration. Moreover, cell proliferation can be also monitored using this technique. The proposed measurement method can determine cell viability without affecting the cellular behaviors during culture. It has a high potential to develop a fast and easy measurement compared with the conventional cellular analysis techniques.

CD4 counting technologies for HIV therapy monitoring in resource-poor settings--state-of-the-art and emerging microtechnologies

Modern advancements in pharmaceuticals have provided individuals who have been infected with the human immunodeficiency virus (HIV) with the possibility of significantly extending their survival rates. When administered sufficiently soon after infection, antiretroviral therapy (ART) allows medical practitioners to control onset of the symptoms of the associated acquired immune deficiency syndrome (AIDS). Active monitoring of the immune system in both HIV patients and individuals who are regarded as "at-risk" is critical in the decision making process for when to start a patient on ART. A reliable and common method for such monitoring is to observe any decline in the number of CD4 expressing T-helper cells in the blood of a patient. However, the technology, expertise, infrastructure and costs to carry out such a diagnostic cannot be handled by medical services in resource-poor regions where HIV is endemic. Addressing this shortfall, commercialized point-of-care (POC) CD4 cell count systems are now available in such regions. A number of newer devices will also soon be on the market, some the result of recent maturing of charity-funded initiatives. Many of the current and imminent devices are enabled by microfluidic solutions, and this review will critically survey and analyze these POC technologies for CD4 counting, both on-market and near-to-market deployment. Additionally, promising technologies under development that may usher in a new generation of devices will be presented.

Real-time and non-invasive impedimetric monitoring of cell proliferation and chemosensitivity in a perfusion 3D cell culture microfluidic chip

A perfusion three-dimensional (3D) cell culture microfluidic chip has been developed for real-time and non-invasive impedimetric monitoring of cell proliferation and chemosensitivity. In this study, human oral cancer cells (OEC-M1) were encapsulated in 3D agarose scaffold and cultured in a miniaturized chamber under perfusion of tested substance. This setting provides a more in vitro physiologically relevant microenvironment to better mimic the complex in vivo microenvironment. A pair of vertical electrodes was embedded at the opposite sidewalls of the culture chamber for the on-site impedance measurement. Cell density in the 3D construct was shown to be proportional to the impedance magnitude of the entire construct. Therefore, perfusion 3D cell culture was performed for up to 5 days and cell proliferation can be monitored by the impedimetric analysis. Moreover, real-time impedimetric monitoring of cell viability under the perfusion of anti-cancer drug in different concentrations was conducted and the impedance magnitude was directly correlated with the cell viability. From the confirmation of the endpoint cell viability assays, a concentration-dependent effect was shown; however, the response of cell viability during the drug treatment was able to be traced by the impedance measurement. The experimental results showed that cell proliferation and chemosensitivity in 3D cell culture format can be monitored by impedance measurement. This microfluidic chip has a high potential to develop a powerful analytical platform for cancer research.

CMOS cell sensors for point-of-care diagnostics

The burden of health-care related services in a global era with continuously increasing population and inefficient dissipation of the resources requires effective solutions. From this perspective, point-of-care diagnostics is a demanded field in clinics. It is also necessary both for prompt diagnosis and for providing health services evenly throughout the population, including the rural districts. The requirements can only be fulfilled by technologies whose productivity has already been proven, such as complementary metal-oxide-semiconductors (CMOS). CMOS-based products can enable clinical tests in a fast, simple, safe, and reliable manner, with improved sensitivities. Portability due to diminished sensor dimensions and compactness of the test set-ups, along with low sample and power consumption, is another vital feature. CMOS-based sensors for cell studies have the potential to become essential counterparts of point-of-care diagnostics technologies. Hence, this review attempts to inform on the sensors fabricated with CMOS technology for point-of-care diagnostic studies, with a focus on CMOS image sensors and capacitance sensors for cell studies.

Detection of Cryptosporidium in miniaturised fluidic devices

Contamination of drinking water with the protozoan pathogen, Cryptosporidium, represents a serious risk to human health due to the low infectious dose and the resistance of this parasite to chlorine disinfection. Therefore, several countries have legislated for the frequent monitoring of drinking water for Cryptosporidium presence. Existing approved monitoring protocols are however time-consuming and do not provide essential information on the species, virulence or viability of detected oocysts. Rapid, more information-rich and automatable systems for Cryptosporidium detection are highly sought-after, and numerous miniaturised devices have been developed to address this need. This review article aims to summarise the state-of-the-art and compare the performance of these systems in terms of detection limit, ability to determine species, viability and performance in the presence of interferents. Finally, conclusions are drawn with regard to the most promising methods and directions of future research.

Leukocyte counting from a small amount of whole blood using a size-controlled microcavity array

Absolute counting of total leukocytes or specific subsets within small amounts of whole blood is difficult due to a lack of techniques that enable separation of all leukocytes from limited amounts of whole blood. In this study, a microfluidic device equipped with a size-controlled microcavity array for highly efficient separation of leukocytes from submicroliters of whole blood was developed. The microcavity array can separate leukocytes from whole blood based on differences in the size and deformability between leukocytes and other blood cells. Leukocytes recovered on aligned microcavities were continuously processed for image-based immunophenotypic analysis. Our device successfully recovered over 90% of leukocytes in 1 µL of whole blood without pretreatment such as density gradient centrifugation or erythrocyte lysis. In addition, the proposed system successfully performed absolute enumeration of human CD4(+) and CD8(+) leukocytes from 1 µL of whole blood, and the obtained data showed good correlation with conventional flow cytometric analysis. Our microfluidic device has great potential as a tool for a point-of-care leukocyte analysis system.

Oryza sativa cytochrome P450 family member OsCYP96B4 reduces plant height in a transcript dosage dependent manner

Background

Plant cytochromes P450 are involved in a wide range of biosynthetic reactions and play various roles in plant development. However, little is known about the biological functions of the subfamily CYP96 in plants.

Methodology/Principal Findings

Here, we report a novel semi-dwarf rice mutant, in which a single copy of transposon dissociator (Ds) was inserted into the gene OsCYP96B4 (Oryza sativa Cytochrome P450 96B4). The mutant exhibits the defects in cell elongation and pollen germination, which can be complemented by the wild type OsCYP96B4 and be rescued by remobilization of the Ds element with the presence of the transposase Activator (Ac). Transgenic plants harboring OsCYP96B4 double-stranded RNA interference construct mimicked the mutant phenotype. The oscyp96b4 mutant phenotype could not be rescued by all the tested phytohormones and it was found that OsCYP96B4 reduced plant height in a transcript dosage dependent manner. Heterologous expression of OsCYP96B4 in Schizosaccharomyces pombe resulted in missegregation and wider cells. Further investigation showed that the mutant exhibited the defects in the metabolism of some lipid molecular species when compared with the wild type.

Conclusions/Significance

The oscyp96b4 mutant is a novel rice semi-dwarf mutant. Our data suggest that OsCYP96B4 might be involved in lipid metabolism and regulate cell elongation.

Emerging technologies for point-of-care CD4 T-lymphocyte counting

A CD4 T-lymphocyte count determines eligibility for antiretroviral therapy (ART) in patients recently diagnosed with HIV and also monitors the efficacy of ART treatment thereafter. ART slows the progression of HIV to AIDS. In the developing world, CD4 tests are often performed in centralized laboratories, typically in urban areas. The expansion of ART programs into rural areas has created a need for rapid CD4 counting because logistical barriers can delay the timely dissemination of test results and affect patient care through delay in intervention or loss of follow-up care. CD4 measurement at the point-of-care (POC) in rural areas could help the facilitation of ART and monitoring of treatment. This review highlights recent technology developments with applications towards determining CD4 counts at the POC.

A microfabricated electrical differential counter for the selective enumeration of CD4+ T lymphocytes

We have developed a microfabricated biochip that enumerates CD4+ T lymphocytes from leukocyte populations obtained from human blood samples using electrical impedance sensing and immunoaffinity chromatography. T cell counts are found by obtaining the difference between the number of leukocytes before and after depleting CD4+ T cells with immobilized antibodies in a capture chamber. This differential counting technique has been validated to analyze physiological concentrations of leukocytes with an accuracy of ∼9 cells per µL by passivating the capture chamber with bovine serum albumin. In addition, the counter provided T cell counts which correlated closely with an optical control (R(2) = 0.997) for CD4 cell concentrations ranging from approximately 100 to 700 cells per µL. We believe that this approach can be a promising method for bringing quantitative HIV/AIDS diagnostics to resource-poor regions in the world.

Detection of bacterial cells by impedance spectra via fluidic electrodes in a microfluidic device

In this study, a novel method for detecting bacterial cells in deionized (DI) water suspension is presented by using fluidic electrodes with a hydrodynamic focusing technique. KCl solution was utilized as both sheath flow and fluidic electrodes, and the bacterial suspension was squeezed to form three flowing layers with different conductivities on a microfluidic chip. An impedance analyzer was connected with the KCl solution through two Ag/AgCl wires to apply an AC voltage to fluidic layers within a certain frequency for impedance measurements. Porphyromonas gingivalis and Escherichia coli were detected and linear relationships were found between the impedance and the logarithmic value of the bacterial concentration in certain cell concentration ranges. It is demonstrated that bacterial detection using the microdevice is rapid and convenient, with a chip made of simple flow channels, and the detection sensitivity of cell counting can be tuned by varying the width of the sample flow layer through changing input velocities, showing a detection limit of 10(3) cells mL(-1).

Dielectrophoresis-based cell manipulation using electrodes on a reusable printed circuit board

Particle manipulation based on dielectrophoresis (DEP) can be a versatile and useful tool in lab-on-chip systems for a wide range of cell patterning and tissue engineering applications. Even though there are extensive reports on the use of DEP for cell patterning applications, the development of approaches that make DEP even more affordable and common place is still desirable. In this study, we present the use of interdigitated electrodes on a printed circuit board (PCB) that can be reused to manipulate and position HeLa cells and polystyrene particles over 100 microm thick glass cover slips using DEP. An open-well or a closed microfluidic channel, both made of PDMS, was placed on the glass coverslip, which was then placed directly over the PCB. An AC voltage was applied to the electrodes on the PCB to induce DEP on the particles through the thin glass coverslip. The HeLa cells patterned with DEP were subsequently grown to confirm the lack of any adverse affects from the electric fields. This alternative and reusable platform for DEP particle manipulation can provide a convenient and rapid method for prototyping a DEP-based lab-on-chip system, cost-sensitive lab-on-chip applications, and a wide range of tissue engineering applications.

Integration of semiconductor quantum dots into nano-bio-chip systems for enumeration of CD4+ T cell counts at the point-of-need

Recent humanitarian efforts have led to the widespread release of antiretroviral drugs for the treatment of the more than 33 million HIV afflicted people living in resource-scarce settings. Here, the enumeration of CD4+ T lymphocytes is required to establish the level at which the immune system has been compromised. The gold standard method used in developed countries, based on flow cytometry, though widely accepted and accurate, is precluded from widespread use in resource-scarce settings due to its high expense, high technical requirements, difficulty in operation-maintenance and the lack of portability for these sophisticated laboratory-confined systems. As part of continuing efforts to develop practical diagnostic instrumentation, the integration of semiconductor nanocrystals (quantum dots, QDs) into a portable microfluidic-based lymphocyte capture and detection device is completed. This integrated system is capable of isolating and counting selected lymphocyte sub-populations (CD3+CD4+) from whole blood samples. By combining the unique optical properties of the QDs with the sample handling capabilities and cost effectiveness of novel microfluidic systems, a practical, portable lymphocyte measurement modality that correlates nicely with flow cytometry (R2 = 0.97) has been developed. This QD-based system reduces the optical requirements significantly relative to molecular fluorophores and the mini-CD4 counting device is projected to be suitable for use in both point-of-need and resource-scarce settings.

A microchip approach for practical label-free CD4+ T-cell counting of HIV-infected subjects in resource-poor settings

Simple affordable CD4 cell counting is urgently needed to stage and monitor HIV-infected patients in resource-limited settings. To address the limitations of current approaches, we designed a simple, label-free, and cost-effective CD4 cell counting device using microfluidic technology. We previously described the fabrication of a microfluidic system for high-efficiency isolation of pure populations of CD4+ T cells based on cell affinity chromatography operated under controlled flow. Here, we compare the performance of a microfluidic CD4 cell counting device against standard flow cytometry in 49 HIV-positive subjects over a wide range of absolute CD4 cell counts. We observed a close correlation between CD4 cell counts from the microchip device and measurements by flow cytometry, using unprocessed whole blood from HIV-positive adult subjects. Sensitivities for distinguishing clinically relevant thresholds of 200, 350, and 500 cells/microL are 0.86, 0.90, and 0.97, respectively. Specificity is 0.94 or higher at all thresholds. This device can serve as a functional cartridge for fast, accurate, affordable, and simple CD4 cell counting in resource-limited settings.

Label-Free Impedance Biosensors: Opportunities and Challenges

Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.

Rapid and onsite BOD sensing system using luminous bacterial cells-immobilized chip

A BOD monitoring system based on a bio-chip which immobilized luminous bacterium in micrometer-order holes were arrayed and fabricated by micro-machine techniques, was developed. The acrylic chip (3 cmx3 cm) comprises nine micro-holes (diameter: 700 microm or 1 mm, depth: 100 microm) arranged in a three by three array. Cells of the marine luminous bacterium, Photobacterium phosphoreum IFO 13896, which was grown at 15 degrees C for 15 h, were immobilized with 3% or 15% sodium alginate gel. BOD standard solutions or actual sample solution (approximately 10 microl) was fallen onto the cell-arrayed chip, and then the chip was incubated at 25 degrees C for 25 min. After incubation, bioluminescence from the each hole was gray-scaled and measured by a chemi-imager or newly developed onsite-type-monitoring system using a digital camera and a mobile-type personal computer. BOD values less than 16 ppm could detect by the chip, in particular, linear relationship at the concentrations between 0 and 16 ppm could be observed when luminous cells were immobilized with 3% sodium alginate gel. Steady bioluminescence was observed on the chip in the presence of BOD standard solution (GGA solution) which contained mineral elements. Furthermore, simultaneous detection of BOD values in various samples could be employed in the single chip. These results showed that the monitoring system with bio-chip could achieve high-through-put and onsite BOD detection. Our newly developed onsite-type BOD detection system which was used a digital camera and a (mobile) laptop computer was applied to measure and detect organic pollution due to biodegradable substances in wastewater treatment system. The same performance as the chemi-imager system was obtained for data of bioluminescence. The obtained BOD values showed a similar correlation with that of the conventional method for BOD determination (BOD5). These results suggested for successful achievement of high-though-put and onsite detection of BOD in practical.