Nanopore sensors provide an innovative platform for rapid and label-free biomolecule detection. The analytical information extracted from resistive pulse sensing (RPS) measurement, though powerful ...has several limitations. To address these challenges, various signal conditioning algorithms have been researched which include efficient clustering and classification of data, applying probabilistic models to reduce information overlap and also leveraging transient analysis of ionic current instead of the steady state RPS measurement. Additionally, as the current is typically in few picoampere regime with high transition rates, its faithful measurement requires precision instrumentation like a patch clamp amplifier with low noise and high bandwidth. However, for practical deployment of such systems, it is necessary to develop portable electronic interface. Significant efforts have been directed globally to develop on-chip customized integrated circuits with low noise, high bandwidth amplifiers. Thus, it is absolutely timely and pertinent to conduct a review on the various signal processing schemes and electronic interfaces for single biomolecule identification using nanopores which will enable to comprehend the current status for its deployment as a commercial platform for genomics and ultrasensitive detection. To the best of our knowledge, the data extraction methodologies and electronic interface schemes for nanopores have not yet been summarized. In this paper, a comprehensive review emphasizing the signal processing algorithms for DNA sequencing and protein identification in complex analyte using functionalized and non-functionalized nanopores has been presented along with the on-chip low noise electronic interfaces required for field deployable measurement.
Solid-state nanopore has the ability to detect proteins at a single-molecule level with its high sensitivity, high-throughput, and low cost. Improvements in fabrication, functionalization, and ...characterization of solid-state nanopores keep evolving. Various analytical methods targeted towards diagnostic applications using nanopore-based devices are appearing. This review article provides an overview of recent progress in the field of solid-state and biological nanopores for protein detection in a complex analyte. The advantages and challenges involved in nanopore sensing have been discussed. Further, the review surpasses the steady-state resistive pulse techniques of sensing and incorporate transient variations in the nanopore conductance. Application of the power spectral density of these fluctuations toward sensing has been highlighted with importance on reducing the detection limit in a complex environment. Lastly, the current problems and future perspectives have been discussed with a perspective to increase nanopores performance towards diagnostic applications in complex medium.
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•Overview of recent developments of solid-state and biological nanopores for protein sensing in a complex analyte.•Functionalization strategies of both solid-state and biological nanopores.•Application of the power spectral density of transient nanopore conductance fluctuations in a complex environment.
Affordable point-of-care (PoC) diagnostic devices enable detection of prostate specific antigen (PSA) in resource limited settings. Despite the advancements in PoC systems, most of the reported ...methods for PSA detection have unsatisfactory detection limits and are based on labelled assays, requiring multiple reagent flow steps which increases both expenses and inconvenience. Circumventing these constraints, we report here the development and validation of a label free, affordable dielectrophoresis (DEP) based graphene field effect transistor (FET) sensor implemented using coplanar electrodes and integrated uniquely with a compact disc based microfluidic platform along with electronics readout for the estimation of PSA at the point of care. Design of coplanar gate electrode which has not been explored earlier is not a straightforward approach. In fact, it has been observed that there is a non-monotonic dependence of the capture of PSA molecules in the channel region of the FET with varying widths and spacings of the gate electrode. The graphene FET based PoC device with optimized coplanar gate electrode is the only label free analytical system for PSA detection requiring simple operation and achieving a detection limit of 1 pg/ml in serum with a wide dynamic range upto 4 ng/ml and appreciable selectivity against potential interferents like bovine serum albumin (BSA) and human immunoglobulin G (IgG). Further, it has been validated satisfactorily with commercially available existing systems using human serum samples. Moreover, the proposed sensing system lowers the detection limit by three orders of magnitude compared to a recent study on label free PoC device on other cancer biomarkers.
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•Existing PoC systems for PSA detection use labelled sensors with reagent flow steps, making them costly & difficult for use.•· We propose label free, affordable dielectrophoresis (DEP) based graphene FET sensor implemented using coplanar electrodes.•Unique integration with a CD based microfluidic platform along with electronics readout for estimation of PSA at PoC.•There is a non-monotonic dependence of the capture of PSA molecules with width and spacing of gate electrode.•Proposed PoC is the only label free analytical system for PSA sensing with LOD better than most of the existing reports.•The detection limit is lowered by three orders of magnitude compared to label free PoC device on other cancer biomarkers.
To enable detection and discovery of biomarkers, development of label-free, ultrasensitive, and specific sensors is the need of the hour. For addressing this requirement, here, a Schottky-contacted ...ZnO nanorod biosensor has been demonstrated, which explores the interplay between Schottky junction capacitance and solution resistance, resulting in an interesting sensing principle of competitive impedance spectroscopy. When the transition of dominating impedance occurs from solution resistance to junction capacitance, a notch or a peak appears in the impedance response at a particular frequency (referred to as the corner frequency) depending on the charge of the target molecule. The appearance of the peak or notch acts like an electronic label for selectivity since it is visible only for target molecules even at ultralow concentrations in the physiological analyte, where the magnitude of impedance change overlaps with that for nonspecific molecules. This phenomenon has been successfully applied for the positively charged vascular endothelial growth factor (VEGF) and the negatively charged hepatitis B surface antigen (HBsAg), where the shifts in the higher corner frequencies for 1 aM concentration of the target molecules have been observed to be more than 3 times the changes in the impedance magnitude. Further, the area of the ZnO nanorods was segmented into two zones corresponding to the lower and higher concentration regimes, thereby expanding the dynamic range. To summarize, an ultralow detection limit of 1 aM with a dynamic range up to 1 pM was achieved for VEGF and HBsAg, which is 4 orders of magnitude and 20 times lower than their most sensitive label-free reports, respectively.
Nanopores have been well established as a promising platform for real time stochastic detection of single biomolecules and have made sufficient commercial progress in terms of DNA sequencing. Amongst ...the various strategies for specific protein estimation in physiological analyte, aptamer functionalized nanopores have been reported to quantify proteins down to few picomolars in control solution. In this paper, we explore the quantification of target protein in serum down to picomolar concentration using aptamer functionalized nanopores. For such cases, the current settles to a new value in multiple steps due to the low dissociation constants of the receptors and the final current blockade sensitivity is the primary indicator of target protein concentration. It has been observed that the current sensitivity histograms not only have a statistical variation (due to the fluctuations in the device fabrication) but also overlap significantly between the different concentration ranges in the picomolar regime, which makes quantification challenging. Here, we introduce probabilistic fuzzy model based on Monte Carlo simulation and demonstrate its ability by quantifying thrombin down to 50-pM concentration in undiluted serum. The method has been verified with 25 test solutions and the results reveal the potential of this computational approach toward lowering the detection limit by three orders of magnitude compared with the existing status, thus enabling the functionalized glass nanopore platform makes great progress toward clinical testing.
This paper presents a noise spectroscopy analysis of the current traces recorded in a functionalized silicon oxide nanopore in presence of specific antigen (Hep-B), nonspecific antigen (BSA), and ...their complex mixture for the first time. It is observed that though the on and off dwell times can differentiate nonspecific antigen from specific antigen in pure buffer, an approximate quantification of the specific antigen with low-dissociation constant of the receptor-ligand pair, becomes almost impossible in complex mixture. This has been ascribed to the significant overlap in the current blockade sensitivity values between the different concentration ranges of the specific antigen. On the contrary, a noise spectroscopy analysis shows a Lorentzian spectrum in presence of specific antigen with a distinct shift in the roll-off frequency, such that upto 1-nM BSA concentration; it has been possible to estimate the concentration of the specific antigen even for 1-pM Hep-B. However, for BSA concentration greater than 1 nM, the roll-off frequency for a particular concentration of specific antigen starts deviating from its value in pure buffer and overlaps with other concentration range. This problem has been addressed by processing the fractional change in current blockade and roll-off frequency by a partial least square-discriminant analysis based multivariate statistical model. It has been observed that the learning model yields 91.5% correct classification with the solutions, and has been able to predict the concentration of Hep-B quite closely even for a low value of 1 pM in presence of 100 nM concentration of BSA.
Highlights ► Evidence suggests involvement of pro-inflammatory cytokines in neurodegeneration. ► Pro-inflammatory cytokines are released from activated microglia. ► Cytokines may promote neuronal ...survival or death depending on environment. ► Microglial cytokine release is a viable target in treatment of neurodegeneration.
An understanding of the current change in a solid state nanopore due to particle movement or capture is crucial for improvement of nanopore based sensing technologies. For lower aspect ratio pores, ...which are gaining importance due to their high sensitivity, there is interplay between access and pore resistance and the existing theories for computation of access resistance cannot explain most of the experimental observations. Hence, there is a need to develop a comprehensive model for calculating the effective conductance drop in presence of particles in a solid state nanopore. In this paper, we develop analytical models to calculate both the access and pore resistance in presence of particle at different positions during translocation and also when captured by receptors in functionalized nanopores. A wide range of pore geometry and molar strength has been investigated. Taking into consideration the positional uncertainty during particle translocation, the effective resistance sensitivity has been found to agree very well with the experimental observations in low aspect ratio pore. Additionally, we observe that in functionalized nanopores, a pore of higher diameter results in around 50% increase in sensitivity compared to a pore with half its diameter, which indicates the scope of design optimization in such systems.
The incidence of acute and chronic spinal cord injury (SCI) in the United States is more than 10,000 per year, resulting in 720 cases per million persons enduring permanent disability each year. The ...economic impact of SCI is estimated to be more than 4 billion dollars annually. Preclinical studies, case reports, and small clinical trials suggest that early treatment may improve neurological recovery. To date, no proven therapeutic modality exists that has demonstrated a positive effect on neurological outcome. Emerging data from recent preclinical and clinical studies offer hope for this devastating condition. This review gives an overview of current basic research and clinical studies for the treatment of SCI.
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