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Step emulsification (SE), which generates droplets by a sharp change in confinement, has emerged as a potential alternative to flow-focusing technology. Water/dispersed phase is continuously pumped through a shallow inlet channel into a deep chamber pre-filled with the oil/continuous phase. The need for one or more pumps to maintain a continuous flow for droplet generation, and the consequent use of high sample volumes, limit this technique to research labs. Here, we report a pumpfree SE technique for rapid and high-throughput generation of monodisperse hydrogel (agarose) beads using µl sample volume. Instead of using syringe pumps, we sequentially pipetted oil and liquid agarose into a microfluidic SE device to generate between 20000 and 80000 agarose beads in ∼ 2 min. We also demonstrated the encapsulation of loop-mediated isothermal amplification mixture inside these beads at the time of their formation. Finally, using these beads as reaction chambers, we amplified nucleic acids fromP. falciparumand SARS-CoV-2 inside them. The pump-free operation, tiny sample volume, and high-throughput generation of droplets by SE make our technique suitable for point-of-care diagnostics.

A PortAbs based pathogen nucleic acid detection system using peptide nucleic acid (PNA) and a cyanine dye, DiSc2(5). The shift is measured of the absorbance induced by binding of a PNA probe to a complementary DNA strand using a portable two-color absorption system.

We report a two-layer microfluidic device to study the combined effect of confinement and chemical gradient on the motility of wild typeE. coli. We track individualE. coliin 50μmand 10μmwide channels, with a channel height of 2.5μm, to generate quasi-2D conditions. We find that contrary to expectations, bacterial trajectories are super-diffusive even in absence of a chemical (glucose) gradient. The superdiffusive behaviour becomes more pronounced on introduction of a chemical gradient or on strengthening the lateral confinement. Runlength distributions for weak confinement in absence of chemical gradients follow an exponential distribution. Both confinement and chemoattraction induce deviations from this behaviour, with the runlength distributions approaching a power-law form under these conditions. Both confinement and chemoattraction suppress large angle tumbles as well. Our results suggest that wild-typeE. colimodulates both its runs and tumbles in a similar manner under physical confinement and chemical gradient.

There is a need for widespread testing in India to stop the spread of the novel coronavirus in the population. While RT-PCR is the recommended diagnostic technique, its use is limited to well-equipped laboratories due to the need for specialized instrumentation, reagents and trained personnel. Immunodiagnostic tests are not yet recommended by the WHO for diagnosing active infections. There is a strong need for developing point-of-care molecular tests. Based on our past experience with paperfluidic devices for diagnosing bacterial infections by molecular tests, we propose the development of a diagnostic test for COVID-19. As a platform technology, it could be adapted to other viral outbreaks in future.

Microfluidics deals with fluid flow in micron-sized channels. At least one characteristic dimension of these fluid-carrying channels is in the micron scale (typically from 1 mm to several hundreds of mm), resulting in flows with very small (typically, l 1) Reynolds numbers [1]. The scaling down of the channel dimensions leads to some unique features, such as laminar flow, rapid diffusion, rapid heat transfer, and large surface-area-to-volume ratios.

Detection of bacterial colonies in water is a pressing issue in recent times owing to its implications on human health, leading to an urgent need for low cost, disposable sensors. In this work, we report a disposable impedimetric sensor for detection of total bacterial colonies present in water samples. The sensor consists of a polyaniline coated filter paper functionalized with a homo-bi functional crosslinker, glutaraldehyde. Prior to the functionalization step, two Ag electrodes are deposited on the filter paper using conductive silver paste. The aldehyde groups of glutaraldehyde bind with the amine functional groups present on bacterial cell wall resulting in a change in dielectric constant, and consequently, the capacitive effect between the two Ag electrodes. Also, bacterial metabolism affects the medium conductivity and in turn, the medium resistance changes. The combined effect of changes in capacitive effect as well as resistance is reflected as a change in AC impedance measured using a frequency response analyzer (FRA). E. coli and Pseudomonas aeruginosa bacteria are detected in PBS buffer up to ~ 500 cfu/mL. Testing is also carried out by spiking tap water and grey water with known concentrations of bacteria samples. The detection limits obtained are 500 – 1000 cfu/mL with a response time of ~ 20 minutes. The developed sensor provides rapid, moderately sensitive, cost-effective solution for detecting total bacterial load in water samples.

We developed a model for a universal gradient generator to obtain gradients of different functional forms by changing only the inlet flow rates.

Developing sensors for food safety, soil analysis, water quality monitoring and healthcare often requires distinguishing between different species of bacteria. The most rapid, sensitive and specific method to identify bacteria is to analyse their DNA sequence, which comprises of disinfection and lysis of bacterial cells, amplification of the isolated DNA and detection of the amplified sequence. Seamless integration of these steps on a paper substrate is a big challenge. This problem is even more complex for mycobacteria as its thick cell wall structure impedes lysis and the high GC-content of the genome requires careful optimization of enzymatic denaturation. Here we successfully combine thermal lysis and loop-mediated isothermal amplification (LAMP) into a single reaction step on paper. We demonstrate our integrated assay by amplifying DNA from 100 CFU/mL of Escherichia coli (MG1655) and Mycobacterium smegmatis (mc2155) cells in 30 min on a paper substrate. We also confirm that E. coli and M. smegmatis can be completely disinfected on paper by heating at 60 °C for 5 min and 15 min respectively, making this assay safe and suitable for incorporation into diverse paperfluidic sensors for field use.

Molecular self-assembly plays a vital role in various biological functions. However, when aberrant molecules self-assemble to form large aggregates, it can give rise to various diseases. For example, sickle cell disease and Alzheimer’s disease are caused by self-assembled hemoglobin fibers and amyloid plaques, respectively. Here, we study the assembly kinetics of such fibers using kinetic Monte Carlo simulation. We focus on the initial lag time of these highly stochastic processes, during which self-assembly is very slow. The lag time distributions turn out to be similar for two very different regimes of polymerization, namely, (a) when polymerization is slow and depolymerization is fast and (b) the opposite case, when polymerization is fast and depolymerization is slow. Using temperature-dependent on- and off-rates for hemoglobin fiber growth, reported in recent in vitro experiments, we show that the mean lag time can exhibit non-monotonic behavior with respect to the change in temperature.

Molecular self-assembly plays vital role in various biological functions. However, when aberrant molecules self-assemble to form large aggregates, it can give rise to various diseases. For example, the sickle cell disease and Alzheimer’s disease are caused by self-assembled hemoglobin fibers and amyloid plaques, respectively. Here we study the assembly kinetics of such fibers using kinetic Monte-Carlo simulation. We focus on the initial lag time of these highly stochastic processes, during which self-assembly is very slow. The lag time distributions turn out to be similar for two very different regimes of polymerization, namely, a) when polymerization is slow and depolymerization is fast, and b) the opposite case, when polymerization is fast and depolymerization is slow. Using temperature dependent on- and off-rates for hemoglobin fiber growth, reported in recent in-vitro experiments, we show that the mean lag time can exhibit non-monotonic behaviour with respect to change of temperature.

In sickle cell anemia patients, red blood cells (RBCs) are known to become sickle shaped and stiff under hypoxic conditions as a consequence of hemoglobin polymerization. While RBC shape can discriminate sickle blood from healthy, it has not been used until now as a sole biophysical marker to differentiate between homozygous (disease) and heterozygous (trait) sickle blood samples. Here, we establish a technique based on the differential response of disease and trait RBCs to chemically-induced hypoxia to distinguish between these samples for the first time. By comparing the RBC shape distributions in blood treated with high and low concentrations of the hypoxia-inducing agent, we correctly identify 35 unknown blood samples as healthy, sickle cell disease or trait. Finally, we demonstrate our image-based classification technique with a portable smartphone microscope and a disposable microfluidic chip as a prospective point-of-care device enabling fast and confirmed diagnosis of sickle cell anemia. Significance statement Red blood cells (RBCs) of individuals with sickle cell anemia exhibit characteristic shapes in low oxygen environments. The shape of a sickle RBC is determined by its hemoglobin content and how fast oxygen is removed from its surroundings. We report a technique to distinguish between sickle cell carriers and individuals with sickle cell anemia within an hour by treating whole blood with a chemical that removes oxygen, imaging the blood sample inside a microfluidic chamber using a smartphone microscope and finally comparing the shapes of the sickle cells using a classification scheme. We demonstrate the proof of concept of a biophysical test based on the analysis of RBC shapes for point-of-care diagnosis of sickle cell disease in low resource settings.

Cardiac biomarker detection helps in early diagnosis of cardiac syndromes. However, a rapid, cost-effective, reliable, and easy-to-use sensor is still unavailable. Herein, we report a disposable, label free, impedance-based biosensor for the detection of two common cardiac biomarkers, Myoglobin (Myo), and Myeloperoxidase (MPO). The sensor is fabricated on Whatman filter paper coated with a conducting polymer, polyaniline (PAni). The PAni-coated paper is functionalized with glutaraldehyde, a homo-bi functional crosslinker, prior to the covalent attachment of antibodies specific to each biomarker protein. Non-specific active regions of the sensor are blocked by treatment with bovine serum albumin. Conductive silver paste is used to define electrodes for AC impedance measurement on the PAni coated filter paper. Binding of the target protein (Myo or MPO) to the specific antibody changes the impedance between the electrodes; this is detected using AC impedance spectroscopy. The impedance is measured using a frequency response analyzer with an AC excitation voltage of 100 mV in the frequency range of 100 Hz–100 kHz. We can successfully detect Myo and MPO in buffer solution within the concentration range of 100 ng/mL– $50~\mu \text{g}$ /mL. Detection limit obtained for these cardiac biomarkers spiked in human serum is $1~\mu \text{g}$ /mL. Further blocking using human serum improves the lower detection limit to 500 ng/mL. The developed biosensor uses inexpensive materials and fabrication techniques, detects cardiac biomarkers in clinically relevant concentrations rapidly (i.e., within 20 mins), and can be disposed in an environment friendly manner, thus making the sensor suitable for diagnostic applications.

This paper reports for the first time printed-circuit-board (PCB)-based label-free electrochemical detection of bacteria. The demonstrated immunosensor was implemented on a PCB sensing platform which was designed and fabricated in a standard PCB manufacturing facility. Bacteria were directly captured on the PCB sensing surface using a specific, pre-immobilized antibody. Electrochemical impedance spectra (EIS) were recorded and used to extract the charge transfer resistance (Rct) value for the different bacteria concentrations under investigation. As a proof-of-concept, Streptococcus mutans (S. mutans) bacteria were quantified in a phosphate buffered saline (PBS) buffer, achieving a limit of detection of 103 CFU/mL. Therefore, the proposed biosensor is an attractive candidate for the development of a simple and robust point-of-care diagnostic platform for bacteria identification, exhibiting good sensitivity, high selectivity, and excellent reproducibility.

We report a microfluidic device to determine the shear elastic modulus and the Young’s modulus of red blood cells (RBCs). Our device consists of a single channel opening into a funnel, with a semi-circular obstacle placed at the mouth of the funnel. As a RBC passes the obstacle, it deflects from its original path. Using populations of artificially-stiffened RBCs, we show that the stiffer RBCs deflect more compared to the normal RBCs. We use calibration curves obtained from numerical simulations to map a trajectory of each RBC to its elastic constants. Our estimates of the shear elastic modulus and the Young’s modulus of normal RBCs are within the same range of values reported in the literature using AFM, optical tweezers and micropipette measurements. We also estimate indirectly the elongation index of normal and artificially hardened RBCs from their tracks, without any direct observation of their shapes. Finally, we sort a mixed population of RBCs based on their deformability alone. Our device could potentially be further miniaturized to sort and obtain the elastic constants of nanoscale objects, whose shape change is difficult to monitor by optical microscopy.

Developing sensors in the domains of food safety, soil analysis, water quality monitoring and healthcare often requires distinguishing between different species of bacteria. The most rapid, sensitive and specific method to identify bacteria is by analysing their DNA sequence, which comprises of disinfection and lysis of bacterial cells, amplification of the isolated DNA and detection of the amplified sequence. Seamless integration of these assays on a paper substrate remains a big challenge in paperfluidic nucleic acid analyis. Combining lysis and isothermal amplification in a single reaction step is difficult because the porosity of paper and the presence of cell debris following lysis reduces the efficiency of DNA amplification. On the other hand, extracting and purifying the DNA after lysis to improve the amplification efficiency involves addition of chemical reagents, one or more wash steps and manual intervention. This problem is even more complex for mycobacteria as its thick cell wall structure impedes lysis and the high GC-content of the genome requires careful optimization of enzymatic denaturation during isothermal amplification. Here we successfully combine thermal lysis and loop-mediated isothermal amplification (LAMP) into a single reaction step on paper without the need for any intermediate intervention. We demonstrate our integrated assay by amplifying DNA from 100 CFU/mL ofEscherichia coli(MG1655) andMycobacterium smegmatis(mc2155) cells in 30 min on a paper substrate. We also confirm thatE. coliandM. smegmatiscan be completely disinfected on paper by heating at 60 °C for 5 min and 15 min respectively, making this assay safe and suitable for incorporation into diverse paperfluidic sensors for field use.Electronic Supplementary Information (ESI) is available.

Paper-based microfluidics has been extensively used in recent times to perform automated multi-step reactions. One of the requirements to carry out sequential reactions is the ability to control the fluid flow accurately on paper substrates, comparable to what is achieved in conventional microfluidic devices. Flow control still remains a major roadblock in the translation of more complex paperfluidic devices from research labs into the commercial domain. In this chapter, we describe the advantages and limitations of the reported flow control strategies in paperfluidics. Modelling the flow on paper and its implication on the device design are also discussed. Finally, we summarize the challenges for commercialization of these flow-switching devices.

Paper is a versatile platform for several biological assays. One of the most popular assays performed on paper substrates is the nucleic acid amplification test (NAAT). Compared to other diagnostic techniques, NAATs are specific, sensitive and fast. While the polymerase chain reaction (PCR) is still the most widely-used technique for amplifying nucleic acids, isothermal DNA amplification techniques have emerged as viable alternatives to PCR on paper. Many innovative detection techniques have also been employed to detect the amplified DNA on paper. There are three main aspects of nucleic acid analysis on paper, namely (a) sample preparation to extract the nucleic acids from cells, (b) amplification of DNA, and (c) detection of the amplified DNA. In this chapter, we will review various amplification techniques in detail. We will also briefly cover the mechanisms to detect the amplified nucleic acids on paper. Finally, we will discuss the potential of these technologies to be translated to the point of care.

A disposable filter paper based electronic tongue using different conducting polymers is developed in this work. Sensors were prepared using Whatman filter papers of dimensions 6 mm × 5 mm coated with different conducting polymers (polyaniline and polypyrrole, both in doped and de-doped form). Two Ag electrodes were deposited with a separation of 4 mm for AC impedance spectroscopic measurements in the frequency range of 10 Hz – 10 kHz with a 100 mV excitation voltage. The developed sensor was subjected to different concentrations of four basic tastants i.e., salty, sweet, sour and umami. The sensitivity of the sensor was found to be better than the human tongue for all the different tastants. The sensors were also used to differentiate between different water samples and fruit juices, with a promising potential for use in food quality monitoring. Use of principal component analysis on the impedance data aided in formation of clusters, thus distinguishing different types of water samples.

We have amplified an 84 bp fragment from the insertion sequence IS6110 of Mycobacterium tuberculosis (MTB) DNA on a paper substrate in 10 min. Tuberculosis (TB) is a highly infectious disease with a high mortality rate in the developing countries. Cheap and rapid screening assays are needed at the point of care for timely intervention and treatment. While PCR-based detection of TB is faster than bacterial culture and more specific compared to microscopy, PCR is not viable as a routine screening test in many low-income countries where TB is endemic due to the requirement of an expensive thermocycler. Disease screening based on isothermal amplification techniques is, therefore, being explored as an alternative to PCR. Successful isothermal amplification of DNA from HIV, H1N1, Chlamydia trachomatis, E. coli, etc. on cheap and disposable paper substrates has been reported in the literature. Isothermal amplification of MTB DNA on paper has been challenging due to the high GC content (65%) of MTB genome. Here we report helicase dependent amplification of a fragment of MTB DNA on a paper substrate in 10 min starting from 100 copies of the template using inexpensive heat sources, such as hot plates and hand warmers. The enzyme mix used to amplify DNA can be spotted and stored dry on paper at ambient temperatures for more than a month. The DNA amplified on paper can be detected by incorporating a suitable fluorescence marker in the reaction mixture or by directly loading the paper in a standard gel electrophoresis set up. Finally, as a surrogate to real clinical sputum samples, MTB DNA was successfully amplified on paper in the viscous environment of artificial sputum.

Pillar-based passive microfluidic devices combine the advantages of simple designs, small device footprint, and high selectivity for size-based separation of blood cells. Most of these device designs have been validated with dilute blood samples. Handling whole blood in pillar-based devices is extremely challenging due to clogging. The high proportion of cells (particularly red blood cells) in blood, the varying sizes and stiffness of the different blood cells, and the tendency of the cells to aggregate lead to clogging of the pillars within a short period. We recently reported a radial pillar device (RAPID) design for continuous and high throughput separation of multi-sized rigid polystyrene particles in a single experiment. In the current manuscript, we have given detailed guidelines to modify the design of RAPID for any application with deformable objects (e.g. cells). We have adapted RAPID to work with whole blood without any pre-processing steps. We were successful in operating the device with whole blood for almost 6 h, which is difficult to achieve with most pillar-based devices. The availability of multiple parallel paths for the cells and the provision for a self-generating cross flow in the device design were the main reasons behind the minimal clogging in our device. We also observed that a vibrator motor attached to the inlet tubing occasionally disturbed the cell clumps. As an illustration of the improved device design, we demonstrated up to similar to 60-fold enrichment of platelets.

Understanding the regulatory landscape of human cells requires the integration of genomic and epigenomic maps, capturing combinatorial levels of cell type-specific and invariant activity states.Here, we segmented whole-genome bisulfite sequencing-derived methylomes into consecutive blocks of co-methylation (COMETs) to obtain spatial variation patterns of DNA methylation (DNAm oscillations) integrated with histone modifications and promoter-enhancer interactions derived from promoter capture Hi-C (PCHi-C) sequencing of the same purified blood cells.Mapping DNAm oscillations onto regulatory genome annotation revealed that enhancers are enriched for DNAm hyper-oscillations (>30-fold), where multiple machine learning models support DNAm as predictive of enhancer location. Based on this analysis, we report overall predictive power of 99% for DNAm oscillations, 77.3% for DNaseI, 41% for CGIs, 20% for UMRs and 0% for LMRs, demonstrating the power of DNAm oscillations over other methods for enhancer prediction. Methylomes of activated and non-activated CD4+ T cells indicate that DNAm oscillations exist in both states irrespective of activation; hence they can be used to determine the location of latent enhancers.Our approach advances the identification of tissue-specific regulatory elements and outperforms previous approaches defining enhancer classes based on DNA methylation.

In this paper, we present a novel method of fabricating nearly hemispherical polymer lenses using water droplets as moulds. Owing to the naturally forming meniscus of water, the surface of the lens is smooth. This technique allowed us to fabricate small lenses of diameter approximate to 1 mm, which makes them easy to integrate with lab-on-chip platforms. The focal length of the convex lenses was estimated to be approximate to 1 mm. Due to their hemispherical nature, these lenses have a high numerical aperture. The method is simple and cost effective as it eliminates the need for specialized and expensive equipment such as surface plasma cleaner. We fabricated both concave and convex lenses in polydimethylsiloxane (PDMS) using water droplets and PDMS lenses as moulds.

Aspherical optical lenses are known for high performance and aberration free imaging. They are increasingly in demand for developing simple and compact high quality optical systems. The conventional methods of production of aspherical lenses are complex and time-consuming. There is a need for a simple, inexpensive and robust method of fabrication of such lenses. Here, we present a novel, low cost and simple approach to fabricate aspherical lenses reproducibly. The two-step process involves 1) controlled wetting of a curved surface with a transparent, cross-linkable polymer by dipping, and 2) pulling the wetted curved surface from the polymer solution. The curvature of the lens is dependent on the area of wetting, speed of pulling and the curvature of the curved surface. The lenses are produced with less than 5% error, and hence, the approach is reproducible in comparison to the previously reported techniques. A smartphone microscope developed using one of the fabricated lenses is found to have a resolution of ~1.7 μm. In addition, we show an application of these lenses as a means to check for the authenticity of Indian currency notes by a common man. The micro-patterns on the currency note are imaged using the smartphone microscope in ambient light. Also, the lenses have potential applications in developing compact and portable high quality optical systems, such as, endoscopes and microscopes.

Tuberculosis (TB) is a leading cause of high mortality rates in developing countries. Sample preparation is one of the major challenges in developing an inexpensive point-of-care device for rapid and confirmed detection of tuberculosis. Existing chemical and mechanical lysis methods are unsuitable for field applications, as they require intermediate wash steps, manual intervention or separate lysis equipment. We report a one-step reaction protocol (65°C and 60min) for the H37Rv strain of Mycobacterium tuberculosis that (i) completely disinfects the mycobacteria culture, (ii) lyses the cells and (iii) performs helicase dependent amplification on the extracted DNA. Our assay combines multiple functions in a single step, uses a dry heat bath and does not require any intermediate user intervention, which makes it suitable for use by minimally trained health workers at the point of care.

Many common and inexpensive materials, such as, paper, fabric and thread are currently being explored as alternate substrates for low-cost and field-based sensing applications. While these substrates have primarily been utilized to develop low-cost diagnostic devices, it is important to study whether these materials are suitable for more general chemical sensing applications. Here, we report chemical syntheses (inorganic and organic) and sensing using threads as microchannels. We first characterized the liquid transport through thread channels and then measured typical sample losses due to adsorption and evaporation. Next, we demonstrated synthesis of ferric hydroxide in a Y-geometry thread reactor and detected the product by colorimetry. Our low-cost device gave a product yield of 84% compared to a test tube-based synthesis. We also synthesized (with similar to 72% yield) and detected colorless 2,4-dichloro-N-(2-morpholinoethyl) benzamide in an attempt to demonstrate an organic reaction in a thread device. Finally, we successfully detected bovine serum albumin and the glucose present in blood plasma as examples of detection of chemical substances relevant in diagnostics. Our results indicate that cotton and silk threads are indeed suitable materials for incorporation into field-deployable disposable chemical reaction and sensing systems. (C) 2013 Elsevier B.V. All rights reserved.

A complete understanding of phagocytosis requires insight into both its biochemical and physical aspects. One of the ways to explore the physical mechanism of phagocytosis is to probe whether and how the target properties (e.g., size, shape, surface states, stiffness, etc.) affect their uptake. Here we report an imaging-based method to explore phagocytosis kinetics, which is compatible with real-time imaging and can be used to validate existing reports using fixed and stained cells. We measure single-event engulfment time from a large number of phagocytosis events to compare how size and shape of targets determine their engulfment. The data shows an increase in the average engulfment time for increased target size, for spherical particles. The uptake time data on nonspherical particles confirms that target shape plays a more dominant role than target size for phagocytosis: Ellipsoids with an eccentricity of 0.954 and much smaller surface areas than spheres were taken up five times more slowly than spherical targets.

A multicomponent magneto-dendritic nanosystem (MDNS) is designed for rapid tumor cell targeting, isolation, and high-resolution imaging by a facile bioconjugation approach. The highly efficient and rapid-acting MDNS provides a convenient platform for simultaneous isolation and high-resolution imaging of tumor cells, potentially leading towards an early diagnosis of cancer.

Proteins mediate the bulk of biological activity and are powerfully assayed in the diagnosis of diseases. Protein detection relies largely on antibodies, which have significant technical limitations especially when immobilized on two-dimensional surfaces. Here, we report the integration of peptide aptamers with extended gate metal-oxide-semiconductor field-effect transistors (MOSFETs) to achieve label-free sub-picomolar target protein detection. Specifically, peptide aptamers that recognize highly related protein partners of the cyclin-dependent kinase (CDK) family are immobilized on the transistor gate to enable human CDK2 to be detected at 100 fM or 5 pg/mL, well within the clinically relevant range. The target specificity, ease of fabrication, and scalability of these FET arrays further demonstrate the potential application of the multiplexable field effect format to protein sensing.

Miniature lenses can transform commercial imaging systems, e.g., smartphones and webcams, into powerful, low-cost, handheld microscopes. To date, the reproducible fabrication of polymer lenses is still a challenge as they require controlled dispensing of viscous liquid. This paper reports a reproducible lens fabrication technique using liquid mold with programmable curvature and off-the-shelf materials. The lens curvature is controlled during fabrication by tuning the curvature of an interface of two immiscible liquids [polydimethylsiloxane (PDMS) and glycerol]. The curvature control is implemented using a visual feedback system, which includes a software-based guiding system to produce lenses of desired curvature. The technique allows PDMS lens fabrication of a wide range of sizes and focal lengths, within 20 min. The fabrication of two lens diameters: 1 and 5 mm with focal lengths ranging between 1.2 and 11 mm are demonstrated. The lens surface and bulk quality check performed using X-ray microtomography and atomic force microscopy reveal that the lenses are suitable for optical imaging. Furthermore, a smartphone microscope with similar to 1.4-mu m resolution is developed using a self-assembly of a single high power fabricated lens and microaperture. The lenses have various potential applications, e.g., optofluidics, diagnostics, forensics, and surveillance. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Label-free electrical detection of protein interactions has been achieved by direct measurement of variations in open circuit potential (OCP) using an accurate differential voltage measurement. Our model system involves a panel of peptide aptamers that recognise specific protein partners of the cyclin-dependent kinase (CDK) family. Different peptide aptamers immobilized on gold electrodes were used for the detection of human CDK2 and CDK4. The formation of the peptide aptamer recognition layer and the efficiency of its interaction with CDK proteins in yeast cell lysates were characterized by quartz crystal microbalance measurements. The interaction of the peptide aptamers with CDK proteins was successfully detected by direct OCP measurements. The OCP dependence on the pH of the measurement buffer confirms that the effects observed are due to the change in charge upon protein interaction. Variations in charge transfer resistance and in protein/double-layer capacitance were investigated by means of electrochemical impedance spectroscopy with charged redox markers in solution. The present work shows that electrical detection of protein interactions can be achieved by direct measurement of OCP variations using suitable differential voltage instrumentation. The results indicate that label-free detection of protein interactions is possible with potentiometric transducers such as field-effect transistors.