Simultaneous DNA amplification and detection using a pH-sensing semiconductor system

ISFET Biosensor with Loop-Mediated Isothermal Amplification for Electronic Rapid Detection of Mycoplasma Pneumoniae

Mycoplasma pneumoniae (MP) is the main culprit of community-acquired pneumonia. Commonly used laboratory testing methods have many shortcomings. Serological diagnosis has low sensitivity, causing false negatives, while a quantitative real-time polymerase chain reaction (qPCR) requires large equipment and professional staff. To make up for these shortcomings, we proposed a label-free, low-cost, and small-sized ion-sensitive field-effect transistor (ISFET) array based on a low-buffered loop-mediated isothermal amplification (LAMP) assay. A complementary metal oxide semiconductor (CMOS)-based ISFET array with 512 × 512 sensors was used in this system, which responds specifically to H+ with a sensitivity of 365.7 mV/pH. For on-chip amplification, a low-buffered LAMP system designed for the conserved sequences of two genes, CARDS and gyrB, was applied. The rapid release of large amounts of H+ in the low-buffered LAMP solution led to a speedy increase in electrical signals captured by the ISFET array, eliminating the need for a sophisticated temperature cycling and optical system. The on-chip results showed that the device can accurately complete MP detection with a detection limit of about 103 copies/mL (approximately 1 copy per reaction). In the final clinical validation, the detection results of eight throat swab samples using the ISFET sensors were fully consistent with the clinical laboratory diagnostic outcomes, confirming the accuracy and reliability of the ISFET sensors for use in clinical settings. And the entire process from sample lysis to result interpretation takes about 60 min. This platform has potential to be used for the point-of-care testing (POCT) of pathogen infections, providing a basis for the timely adjustment of diagnosis and treatment plans.

Technical advances in laboratory diagnosis of bloodstream infection

INTRODUCTION

Rapid and accurate laboratory diagnosis is essential for the effective treatment of bloodstream infection (BSI).

AREAS COVERED

This review aims to address novel and traditional approaches that exhibit different performance characteristics in the diagnosis of BSI. In particular, the authors will discuss the pros and cons of the blood culture-based phenotypic methods, nucleic acid-targeted molecular methods, and host response-targeted biomarker detection in the diagnosis of BSI.

EXPERT OPINION

This manuscript summarizes etiologic and host-based techniques in the diagnosis of BSI. Both methods are not mutually exclusive but should be selected based on clinical needs and laboratory conditions to help diagnose BSI more quickly and accurately.

A pH ultra-sensitive hydrated iridium oxyhydroxide films electrochemical sensor for label-free detection of Vibrio parahaemolyticus

Vibrio parahaemolyticus (V. parahaemolyticus) is a major foodborne pathogen, which can cause serious foodborne illnesses like diarrhoea. Rapid on-site detection of foodborne pathogens is an ideal way to respond to foodborne illnesses. Herein, we provide an electrochemical sensor for rapid on-site detection. This sensor utilized a pH-sensitive metal-oxide material for the concurrent isothermal amplification and label-free detection of nucleic acids. Based on a pH-sensitive hydrated iridium oxide oxyhydroxide film (HIROF), the electrode transforms the hydrogen ion compound generated during nucleic acid amplification into potential, so as to achieve a real-time detection. The results can be transmitted to a smartphone via Bluetooth. Moreover, HIROF was applied in nucleic acid device detection, with a super-Nernst sensitivity of 77.6 mV/pH in the pH range of 6.0-8.5, and the sensitivity showed the best results so far. Detection of V. parahaemolyticus by this novel method showed a detection limit of 1.0 × 103 CFU/mL, while the time consumption was only 30 min, outperforming real-time fluorescence loop-mediated isothermal amplification (LAMP). Therefore, the characteristics of compact, portable, and fast make the sensor more widely used in on-site detection.

Simplified Electrochemical Approach for End-Point Yet Quantitative Detection of Nucleic Acids in Resource-Limited Settings

Nucleic acid detection plays a crucial role in various aspects of health care, necessitating accessible and reliable quantification methods, especially in resource-limited settings. This work presents a simplified electrochemical approach for end-point yet quantitative nucleic acid detection. By elevating the concentration of redox species and choosing potential as the signals, we achieved enhanced signal robustness, even in the presence of interfering substances. Leveraging this robustness, we accurately measured pH-induced redox potential changes in methylene blue solution for end-point nucleic acid detection after loop-mediated isothermal amplification (LAMP). Our method demonstrated quantitative detection of the SARS-CoV-2 N gene and human ATCB gene and successful discrimination of the human BRAF V600E mutation, comparable in sensitivity to commercial kits. The developed user-friendly electrochemical method offers a simplified and reliable approach for end-point yet quantitative detection of nucleic acids, potentially expanding the benefits of nucleic acid testing in resource-limited settings.

Two-Stage Mixed-Dye-Based Isothermal Amplification with Ribonuclease-Cleavable Enhanced Probes for Dual-Visualization Detection of SARS-CoV-2 Variants of Interest

Rapid and visual detection of SARS-CoV-2 variants is vital for timely assessment of variant transmission in resource-limited settings. Here, a closed-tube, two-stage, mixed-dye-based isothermal amplification method with ribonuclease-cleavable enhanced probes (REP), termed REP-TMAP, for dual-visualization detection of SARS-CoV-2 variants including JN.1, BA.2, BA.4/5, and Delta is introduced. The first stage of REP-TMAP is reverse transcription recombinase polymerase amplification and the second stage is dual-visualization detection synergistically mediated by the REP and the mixed dyes of cresol red and hydroxy naphthol blue. In REP-TMAP reaction, the color change under ambient light indicates SARS-CoV-2 infection, while the fluorescence change under blue light excitation specifies variant type. On detecting transcribed RNA of SARS-CoV-2 spike gene, this assay is rapid (within 40 min), highly sensitive (10-200 copies per reaction), and highly specific (identification of single-base mutations). Furthermore, the assay has been clinically validated to accurately detect JN.1, BA.2, and BA.4/5 variants from 102 human oropharyngeal swabs. The proposed assay therefore holds great potentials to provide a rapid, dual-visualization, sensitive, specific, point-of-care detection of SARS-CoV-2 variants and beyond.

Development and Comparison of Visual LAMP and LAMP-TaqMan Assays for Colletotrichum siamense

Strawberry anthracnose caused by Colletotrichum spp. has resulted in significant losses in strawberry production worldwide. Strawberry anthracnose occurs mainly at the seedling and early planting stages, and Colletotrichum siamense is the main pathogen in North China, where mycelia, anamorphic nuclei, and conidia produced in the soil are the main sources of infection. The detection of pathogens in soil is crucial for predicting the prevalence of anthracnose. In this study, a visualized loop-mediated isothermal amplification (LAMP) assay and a loop-mediated isothermal amplification method combined with a TaqMan probe (LAMP-TaqMan) assay were developed for the β-tubulin sequence of C. siamense. Both methods can detect Colletotrichum siamense genomic DNA at very low concentrations (104 copies/g) in soil, while both the visualized LAMP and LAMP-TaqMan assays exhibited a detection limit of 50 copies/μL, surpassing the sensitivity of conventional PCR and qPCR techniques, and both methods showed high specificity for C. siamense. The two methods were compared: LAMP-TaqMan exhibited enhanced specificity due to the incorporation of fluorescent molecular beacons, while visualized LAMP solely necessitated uncomplicated incubation at a constant temperature, with the results determined by the color change; therefore, the requirements for the instrument are relatively straightforward and user-friendly. In conclusion, both assays will help monitor populations of C. siamense in China and control strawberry anthracnose in the field.

Digital Sort-Enabled Counting Allows Absolute Electrical Quantification of Target Nucleic Acid

Quantitative nucleic acid amplification tests are of great importance for diagnostics, but current approaches require complex and costly optical setups that limit their nonlaboratory applications. Herein we describe the implementation of a microfluidics platform that can perform binary DNA-amplification-activated droplet sorting. The digital sort-enabled counting (DISCO) platform enables label-free absolute quantification of the nucleic acid. This is achieved by provoking a pH change in droplets through a loop-mediated isothermal amplification (LAMP) reaction, followed by using sorting by interfacial tension (SIFT) to direct positive and negative droplets to different outlets. With the use of on-chip electrodes at both outlets, we demonstrate that the digital electrical counting of target DNA and RNA can be realized. DISCO is a promising approach for realizing sensitive nucleic acid quantification in point-of-care settings.

Time-encoded electrical detection of trace RNA biomarker by integrating programmable molecular amplifier on chip

One of the serious challenges facing modern point-of-care (PoC) molecular diagnostic platforms relate to reliable detection of low concentration biomarkers such as nucleic acids or proteins in biological samples. Non-specific analyte-receptor interactions due to competitive binding in the presence of abundant molecules, inefficient mass transport and very low number of analyte molecules in sample volume, in general pose critical hurdles for successful implementation of such PoC platforms for clinical use. Focusing on these specific challenges, this work reports a unique PoC biosensor that combines the advantages of nanoscale biologically-sensitive field-effect transistor arrays (BioFET-arrays) realized in a wafer-scale top-down nanofabrication as high sensitivity electrical transducers with that of sophisticated molecular programs (MPs) customized for selective recognition of analyte miRNAs and amplification resulting in an overall augmentation of signal transduction strategy. The MPs realize a programmable universal molecular amplifier (PUMA) in fluidic matrix on chip and provide a biomarker-triggered exponential release of small nucleic acid sequences easily detected by receptor-modified BioFETs. A common miRNA biomarker LET7a was selected for successful demonstration of this novel biosensor, achieving limit of detection (LoD) down to 10 fM and wide dynamic ranges (10 pM-10 nM) in complex physiological solutions. As the determination of biomarker concentration is implemented by following the electrical signal related to analyte-triggered PUMA in time-domain instead of measuring the threshold shifts of BioFETs, and circumvents direct hybridization of biomarkers at transducer surface, this new strategy also allows for multiple usage (>3 times) of the biosensor platform suggesting exceptional cost-effectiveness for practical use.

Enhancing Specific Fluorescence In Situ Hybridization with Quantum Dots for Single-Molecule RNA Imaging in Formalin-Fixed Paraffin-Embedded Tumor Tissues

Single-molecule fluorescence in situ hybridization (smFISH) represents a promising approach for the quantitative analysis of nucleic acid biomarkers in clinical tissue samples. However, low signal intensity and high background noise are complications that arise from diagnostic pathology when performed with smFISH-based RNA imaging in formalin-fixed paraffin-embedded (FFPE) tissue specimens. Moreover, the associated complex procedures can produce uncertain results and poor image quality. Herein, by combining the high specificity of split DNA probes with the high signal readout of ZnCdSe/ZnS quantum dot (QD) labeling, we introduce QD split-FISH, a high-brightness smFISH technology, to quantify the expression of mRNA in both cell lines and clinical FFPE tissue samples of breast cancer and lung squamous carcinoma. Owing to its high signal-to-noise ratio, QD split-FISH is a fast, inexpensive, and sensitive method for quantifying mRNA expression in FFPE tumor tissues, making it suitable for biomarker imaging and diagnostic pathology.

Improved Stability of Graphene-Coated CMOS ISFETs for Biosensing

A polymer-assisted graphene transfer method is used to transfer sheets of monolayer and multilayer graphene onto the passivation layer of ion-sensitive field effect transistor arrays. The arrays are fabricated using commercial 0.35 μm complementary metal-oxide-semiconductor (CMOS) technology and contain 3874 pixels sensitive to pH changes on the top silicon nitride surface. By inhibiting dispersive ion transport and hydration of this underlying nitride layer, the transferred graphene sheets help address non-idealities in the sensor response while retaining some pH sensitivity due to the presence of ion adsorption sites. Improvements in hydrophilicity and electrical conductivity of the sensing surface after graphene transfer, as well as in-plane molecular diffusion along the graphene-nitride interface, also greatly improve spatial consistency across an array, allowing for ∼20% more pixels to remain within operating range and enhancing sensor reliability. Multilayer graphene offers a better performance trade-off than monolayer graphene, reducing drift rate by ∼25% and drift amplitude by ∼59% with minimal reduction in pH sensitivity. Monolayer graphene offers slightly better temporal and spatial uniformity in performance of a sensing array, which is associated with the consistency in layer thickness and a lower defect density.

A Multichannel Electrochemical Sensor Interface IC for Bioreactor Monitoring

This research article introduces a novel integrated circuit (IC) designed for bioreactor applications catering to multichannel electrochemical sensing. The proposed IC comprises 2x potentiometric, 2x potentiostat, 2x ISFET channels and 1x temperature channel. The potentiostat channel utilizes a current conveyor-based architecture with a programmable mirroring ratio, enabling an extensive measurement range of 114 dB. The potentiometric channel incorporates a customized electrostatic discharge (ESD) protection circuit to achieve ultra-low input leakage in the picoampere range, while the ISFET channel employs a constant-voltage, constant-current topology for accurate pH measurement. Combined with the die temperature sensor, this IC is well-suited for monitoring bioreactions in real-time. Additionally, all channels can be time-multiplexed to a reconfigurable analog backend, facilitating the conversion of input signals into digital codes. The prototype of the IC is fabricated using 0.18 μm standard CMOS technology, and each channel is experimentally characterized. The interface IC demonstrates a peak power consumption of 22 μW.

The next generation of hybrid microfluidic/integrated circuit chips: recent and upcoming advances in high-speed, high-throughput, and multifunctional lab-on-IC systems

Since the field's inception, pioneers in microfluidics have made significant progress towards realizing complete lab-on-chip systems capable of sophisticated sample analysis and processing. One avenue towards this goal has been to join forces with the related field of microelectronics, using integrated circuits (ICs) to perform on-chip actuation and sensing. While early demonstrations focused on using microfluidic-IC hybrid chips to miniaturize benchtop instruments, steady advancements in the field have enabled a new generation of devices that expand past miniaturization into high-performance applications that would not be possible without IC hybrid integration. In this review, we identify recent examples of labs-on-chip that use high-resolution, high-speed, and multifunctional electronic and photonic chips to expand the capabilities of conventional sample analysis. We focus on three particularly active areas: a) high-throughput integrated flow cytometers; b) large-scale microelectrode arrays for stimulation and multimodal sensing of cells over a wide field of view; c) high-speed biosensors for studying molecules with high temporal resolution. We also discuss recent advancements in IC technology, including on-chip data processing techniques and lens-free optics based on integrated photonics, that are poised to further advance microfluidic-IC hybrid chips.

Classification of nucleic acid amplification on ISFET arrays using spectrogram-based neural networks

The COVID-19 pandemic has highlighted a significant research gap in the field of molecular diagnostics. This has brought forth the need for AI-based edge solutions that can provide quick diagnostic results whilst maintaining data privacy, security and high standards of sensitivity and specificity. This paper presents a novel proof-of-concept method to detect nucleic acid amplification using ISFET sensors and deep learning. This enables the detection of DNA and RNA on a low-cost and portable lab-on-chip platform for identifying infectious diseases and cancer biomarkers. We show that by using spectrograms to transform the signal to the time-frequency domain, image processing techniques can be applied to achieve the reliable classification of the detected chemical signals. Transformation to spectrograms is beneficial as it makes the data compatible with 2D convolutional neural networks and helps gain significant performance improvement over neural networks trained on the time domain data. The trained network achieves an accuracy of 84% with a size of 30kB making it suitable for deployment on edge devices. This facilitates a new wave of intelligent lab-on-chip platforms that combine microfluidics, CMOS-based chemical sensing arrays and AI-based edge solutions for more intelligent and rapid molecular diagnostics.

Enhancing the repeatability and sensitivity of low-cost PCB, pH-sensitive field-effect transistors

Discrete, extended gate pH-sensitive field-effect transistors (dEGFETs) fabricated on printed circuit boards (PCBs) are a low-cost, simple to manufacture analytical technology that can be applied to a wide range of applications. Electrodeposited iridium oxide (IrOx) films have emerged as promising pH-sensitive layers owing to their theoretically high pH sensitivity and facile deposition, but typically exhibit low pH sensitivity or lack reproducibility. Moreover, to date, a combined IrOx and dEGFET PCB system has not yet been realised. In this study, we demonstrate a dEGFET pH sensor based on an extended gate manufactured on PCB that is rendered pH sensitive through an electrodeposited IrOx film, which can reliably and repeatably display beyond-Nernstian pH response. Using a combination of complementary surface analysis techniques, we show that the high pH sensitivity and repeatability of the dEGFETs are dependent on both the chemical composition and critically the uniformity of the IrOx film. The IrOx film uniformity can be enhanced through electrochemical polishing of the extended gate electrode prior to electrodeposition, leading to dEGFETs that exhibit a median pH sensitivity of 70.7 ± 5 mV/pH (n = 56) compared to only 31.3 ± 14 mV/pH (n = 31) for IrOx electrodeposited on non-polished PCB electrodes. Finally, we demonstrate the applicability of these devices by demonstrating the detection and quantification of ampicillin due to β-Lactamase enzyme activity, thus laying the foundation for cheap and ubiquitous sensors which can be applied to a range of global challenges across healthcare and environmental monitoring.

Large-scale nano-biosensing technologies

Nanoscale technologies have brought significant advancements to modern diagnostics, enabling unprecedented bio-chemical sensitivities that are key to disease monitoring. At the same time, miniaturized biosensors and their integration across large areas enabled tessellating these into high-density biosensing panels, a key capability for the development of high throughput monitoring: multiple patients as well as multiple analytes per patient. This review provides a critical overview of various nanoscale biosensing technologies and their ability to unlock high testing throughput without compromising detection resilience. We report on the challenges and opportunities each technology presents along this direction and present a detailed analysis on the prospects of both commercially available and emerging biosensing technologies.

Micro- and nano-devices for electrochemical sensing

Electrode miniaturization has profoundly revolutionized the field of electrochemical sensing, opening up unprecedented opportunities for probing biological events with a high spatial and temporal resolution, integrating electrochemical systems with microfluidics, and designing arrays for multiplexed sensing. Several technological issues posed by the desire for downsizing have been addressed so far, leading to micrometric and nanometric sensing systems with different degrees of maturity. However, there is still an endless margin for researchers to improve current strategies and cope with demanding sensing fields, such as lab-on-a-chip devices and multi-array sensors, brain chemistry, and cell monitoring. In this review, we present current trends in the design of micro-/nano-electrochemical sensors and cutting-edge applications reported in the last 10 years. Micro- and nanosensors are divided into four categories depending on the transduction mechanism, e.g., amperometric, impedimetric, potentiometric, and transistor-based, to best guide the reader through the different detection strategies and highlight major advancements as well as still unaddressed demands in electrochemical sensing.

Graphical Abstract

Detection of YAP1 and AR-V7 mRNA for Prostate Cancer Prognosis Using an ISFET Lab-On-Chip Platform

Prostate cancer (PCa) is the second most common cause of male cancer-related death worldwide. The gold standard of treatment for advanced PCa is androgen deprivation therapy (ADT). However, eventual failure of ADT is common and leads to lethal metastatic castration-resistant PCa. As such, the detection of relevant biomarkers in the blood for drug resistance in metastatic castration-resistant PCa patients could lead to personalized treatment options. mRNA detection is often limited by the low specificity of qPCR assays which are restricted to specialized laboratories. Here, we present a novel reverse-transcription loop-mediated isothermal amplification assay and have demonstrated its capability for sensitive detection of AR-V7 and YAP1 RNA (3 × 10¹ RNA copies per reaction). This work presents a foundation for the detection of circulating mRNA in PCa on a non-invasive lab-on-chip device for use at the point-of-care. This technique was implemented onto a lab-on-chip platform integrating an array of chemical sensors (ion-sensitive field-effect transistors) for real-time detection of RNA. Detection of RNA presence was achieved through the translation of chemical signals into electrical readouts. Validation of this technique was conducted with rapid detection (<15 min) of extracted RNA from prostate cancer cell lines 22Rv1s and DU145s.

Label-free and portable field-effect sensor for monitoring RT-LAMP products to detect SARS-CoV-2 in wastewater

The COVID-19 pandemic caused by the coronavirus SARS-CoV-2 has proven the need for developing reliable and affordable technologies to detect pathogens. Particularly, the detecting the genome in wastewater could be an indicator of the transmission rate to alert on new outbreaks. However, wastewater-based epidemiology remains a technological challenge to develop affordable technologies for sensing pathogens. In this work, we introduce a label-free and portable field-effect transistor (FET)-based sensor to detect N and ORF1ab genes of the SARS-CoV-2 genome. Our sensor integrates the reverse transcription loop-mediated isothermal amplification (RT-LAMP) reaction as a cost-effective molecular detection exhibiting high specificity. The detection relies upon pH changes, due to the RT-LAMP reaction products, which are detected through a simple, but effective, extended-gate FET sensor (EGFET). We evaluate the proposed device by measuring real wastewater samples to detect the presence of SARS-CoV-2 genome, achieving a limit of detection of 0.31 × 10⁻³ ng/μL for end-point measurement. Moreover, we find the ability of the sensor to perform real-time-like analysis, showing that the RT-LAMP reaction provides a good response after 15 min for concentrations as low as 0.37 ng/μL. Hence, we show that our EGFET sensor offers a powerful tool to detect the presence of the SARS-CoV-2 genome with a naked-eye method, in a straightforward way than the conventional molecular methods for wastewater analysis.

Principles and Applications of Loop-Mediated Isothermal Amplification to Point-of-Care Tests

For the identification of nucleic acids, which are important biomarkers of pathogen-mediated diseases and viruses, the gold standard for NA-based diagnostic applications is polymerase chain reaction (PCR). However, the requirements of PCR limit its application as a rapid point-of-care diagnostic technique. To address the challenges associated with regular PCR, many isothermal amplification methods have been developed to accurately detect NAs. Isothermal amplification methods enable NA amplification without changes in temperature with simple devices, as well as faster amplification times compared with regular PCR. Of the isothermal amplifications, loop-mediated isothermal amplification (LAMP) is the most studied because it amplifies NAs rapidly and specifically. This review describes the principles of LAMP, the methods used to monitor the process of LAMP, and examples of biosensors that detect the amplicons of LAMP. In addition, current trends in the application of LAMP to smartphones and self-diagnosis systems for point-of-care tests are also discussed.

Detection of Epidermal Growth Factor Receptor Expression in Breast Cancer Cell Lines Using an Ion-Sensitive Field-Effect Transistor in Combination with Enzymatic Chemical Signal Amplification

A novel strategy for epidermal growth factor receptor (EGFR) detection using a cell-based field-effect transistor (FET) with enzymatic chemical signal amplification is proposed. Four human breast cancer cell lines [BT474, MDA-MB-231 (MM231), MDA-MB-468 (MM468), and MDA-MB-453 (MM453)] were used to compare the expression levels of EGFR. The cells were non-specifically captured on the surface of the gate of the FET, irrespective of their surface antigens. With this configuration, the heterogeneity of the cells would be analyzed using secondary antibodies conjugated to different kinds of enzymes. Four breast cancer cell lines with different levels of EGFR expression were captured on the respective surfaces of the extracellular matrix (ECM) gel-coated gates of the FETs. Glucose oxidase (GOx) was conjugated to the secondary antibody, and the output signals of the cell-based FETs changed depending on the expression levels of EGFR upon addition of glucose. The order of the expression levels of EGFR among the four cell lines, determined with the cell-based FETs, was consistent with the results of fluorescence detection determined by fluorescence-activated cell sorting (FACS). The cell-based FETs are advantageous for miniaturization and in massive parallel analyses of target molecules expressed on the membranes of cells and EVs, and their small size and cost effectiveness for cancer testing could enable their realization in a future liquid biopsy.

Rotational diffusometric sensor with isothermal amplification for ultra-sensitive and rapid detection of SARS-CoV-2 nsp2 cDNA

In the wake of a pandemic, the development of rapid, simple, and accurate molecular diagnostic tests can significantly aid in reducing the spread of infections. By combining particle imaging with molecular assays, a quick and highly sensitive biosensor can readily identify a pathogen at low concentrations. Here, we implement functionalized particle-enabled rotational diffusometry in combination with loop-mediated isothermal amplification for the rapid detection of the SARS-CoV-2 nsp2 gene in the recombinant plasmid as a proof of concept for COVID-19 diagnostics. By analyzing the images of blinking signals generated by these modified particles, the change in micro-level viscosity due to nucleic acid amplification was measured. The high sensitivity of rotational diffusometry enabled facile detection within 10 min, with a limit of detection of 70 ag/μL and a sample volume of 2 μL. Tenfold higher detection sensitivity was observed for rotational diffusometry in comparison with real-time PCR. In addition, the system stability and the effect of temperature on rotational diffusometric measurements were studied and reported. These results demonstrated the utility of a rotational diffusometric platform for the rapid and sensitive detection of SARS-CoV-2 cDNA fragments.

Detection of cell membrane proteins using ion-sensitive field effect transistors combined with chemical signal amplification

The capture and detection of cells expressing a breast-cancer related membrane protein, namely a BT474 cell line expressing HER2, is demonstrated using ion-sensitive field effect transistors (ISFETs). BT474 cells were exposed to anti-HER2 antibodies and urease-conjugated secondary antibodies to induce chemical signal amplification by adding urea.

Diagnosis of disease relevant nucleic acid biomarkers with off-the-shelf devices

Changes in the level of nucleic acids in blood may be correlated with some clinical disorders like cancer, stroke, trauma and autoimmune diseases, and thus, nucleic acids can serve as potential biomarkers for pathological processes. The requirement of technical equipment and operator expertise in effective information readout of modern molecular diagnostic technologies significantly restricted application outside clinical laboratories. The ability to detect nucleic acid biomarkers with off-the-shelf devices, which have the advantages of portability, simplicity, low cost and short response time, is critical to provide a prompt clinical result in circumstances where the laboratory instruments are not available. This review throws light on the current strategies and challenges for nucleic acid diagnosis with commercial portable devices, indicating the future prospect of portable diagnostic devices and making a great difference in improving the healthcare and disease surveillance in resource-limited areas.

Portable real-time colorimetric LAMP-device for rapid quantitative detection of nucleic acids in crude samples

Loop-mediated isothermal amplification is known for its high sensitivity, specificity and tolerance to inhibiting-substances. In this work, we developed a device for performing real-time colorimetric LAMP combining the accuracy of lab-based quantitative analysis with the simplicity of point-of-care testing. The device innovation lies on the use of a plastic tube anchored vertically on a hot surface while the side walls are exposed to a mini camera able to take snapshots of the colour change in real time during LAMP amplification. Competitive features are the rapid analysis (< 30 min), quantification over 9 log-units, crude sample-compatibility (saliva, tissue, swabs), low detection limit (< 5 copies/reaction), smartphone-operation, fast prototyping (3D-printing) and ability to select the dye of interest (Phenol red, HNB). The device’s clinical utility is demonstrated in cancer mutations-analysis during the detection of 0.01% of BRAF-V600E-to-wild-type molecules from tissue samples and COVID-19 testing with 97% (Ct < 36.8) and 98% (Ct < 30) sensitivity when using extracted RNA and nasopharyngeal-swabs, respectively. The device high technology-readiness-level makes it a suitable platform for performing any colorimetric LAMP assay; moreover, its simple and inexpensive fabrication holds promise for fast deployment and application in global diagnostics.

Recombinase polymerase amplification in minimally buffered conditions

Application of recombinase polymerase amplification (RPA) for pH-based detection of DNA amplification has been investigated. Commercial RPA kits from TwistDx are modified to minimize their pH buffering capacity. Due to the RPA's unique biochemistry, removal of tris from the amplification kit is not enough to lower the buffering capacity of the RPA assay. Even in the absence of tris, RPA components in the commercial kit intrinsically buffer the pH. We show different strategies to minimize the buffering capacity of the RPA kit, while maintaining the amplification efficiency. Even in minimally buffered conditions, it is noticed that RPA's amplification yield is not high enough to overcome the assay's intrinsic buffering capacity. The effect of pyrophosphate precipitation in RPA on the reaction's pH have also been addressed. In conclusion, this work highlights strategies and considerations for the development of pH-based assays from nucleic acid amplification methods which involve ancillary enzymes that catalyze nucleotide hydrolysis.

pH-EVD: A pH-Paper-Based Extraction and Visual Detection System for Instrument-Free SARS-CoV-2 Diagnostics

The ongoing pandemic of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused millions of deaths worldwide. However, most SARS-CoV-2 detection methods depend on time-consuming sample preparation and large detection instruments. Herein, a method employing nonbleeding pH paper to achieve both RNA extraction and visual isothermal amplification is proposed, enabling rapid, instrument-free SARS-CoV-2 detection. By taking advantage of capillary forces, pH-paper-based RNA extraction can be accomplished within 1 min without need for any equipment. Further, the pH paper can mediate dye-free visual isothermal amplification detection. In less than a 46-min sample-to-answer time, pH-paper-based extraction and visual detection (termed pH-EVD) can consistently detect 1200 genome equivalents per microliter of SARS-CoV-2 in saliva, which is comparable to TaqMan probe-based quantitative reverse transcription PCR (RT-qPCR). Through coupling with a chemically heated incubator called a smart cup, the instrument-free, pH-EVD-based SARS-CoV-2 detection method on 30 nasopharyngeal swab samples and 33 contrived saliva samples is clinically validated. Thus, the pH-EVD method provides simple, rapid, reliable, low-cost, and instrument-free SARS-CoV-2 detection and has the potential to streamline onsite COVID-19 diagnostics.

Ultrasensitive Picomolar Detection of Aqueous Acids in Microscale Fluorescent Droplets

We report on a fluorescent-droplet-based acid-sensing scheme that allows limits of detection below 100 pM for weak acids. The concept is based on a strong partitioning of acid from an aqueous phase into octanol droplets. Using salicylic acid as a demonstration, we show that at a high concentration, the acid partitions into the organic phase by a factor of 260, which is approximately consistent with literature values. However, at lower concentrations, we obtain a partition coefficient as high as 10⁶, which is partly responsible for the excellent sensing performance. The enhanced equilibrium partitioning is likely due to the interaction of the dissociated acid phase with the sensor dye employed for this work. The effect of droplet size was determined, after which we derived a simple model to predict the time dependence of the color change as a function of droplet size. This work shows that color-change fluorescent-droplet-based detection is a promising avenue that can lead to exceptional sensing performance from an aqueous analyte.

Nitrates in the environment: A critical review of their distribution, sensing techniques, ecological effects and remediation

Nitrate pollution is eminent in almost all the developing nations as a result of increased natural activities apart from anthropogenic pollution. The release of nitrates in more than critical quantities into the water bodies causes accretion impacts on living creatures, environmental receptors, and human vigour by accumulation through the food chain. Nitrates have recently acquired researchers' huge attention and extend their roots in environmental contamination of surface and groundwater systems. The presence of nitrate in high concentrations in surface and groundwater triggers several health problems, for instance, methemoglobinemia, diabetes, eruption of infectious disorders, harmfully influence aquatic organisms. Sensing nitrate is an alternate option for monitoring the distribution of nitrate in different water bodies. Here we review electrochemical, spectroscopic, and electrical modes of nitrate sensing. It is concluded that, among the various sensors discussed in this review, FET sensors are the most desirable choice. Their sensitivity, ease of use and scope for miniaturisation are exceptional. Advanced functional materials need to be designed to satiate the growing need for environmental monitoring. Different sources of nitrate contamination in ground and surface water can be estimated using different techniques such as nitrate isotopic composition, co contaminants, water tracers, and other specialized techniques. This review intends to explore the research work on remediation of nitrate from wastewater and soil using different processes such as reverse osmosis, chemical denitrification, biological denitrification, ion exchange, electrodialysis, and adsorption. Denitrification proves as a promising alternative over previously reported techniques in terms of their nitrate removal because of its high cost-effectiveness.

Transcript host-RNA signatures to discriminate bacterial and viral infections in febrile children

Traditional laboratory markers, such as white blood cell count, C-reactive protein, and procalcitonin, failed to discriminate viral and bacterial infections in children. The lack of an accurate diagnostic test has a negative impact on child's care, limiting the ability of early diagnosis and appropriate management of children. This, on the one hand, may lead to delayed recognition of sepsis and severe bacterial infections, which still represent the leading causes of child morbidity and mortality. On the other hand, this may lead to overuse of empiric antibiotic therapies, particularly for specific subgroups of patients, such as infants younger than 90 days of life or neutropenic patients. This approach has an adverse effect on costs, antibiotic resistance, and pediatric microbiota. Transcript host-RNA signatures are a new tool used to differentiate viral from bacterial infections by analyzing the transcriptional biosignatures of RNA in host leukocytes. In this systematic review, we evaluate the efficacy and the possible application of this new diagnostic method in febrile children, along with challenges in its implementation. Our review support the growing evidence that the application of these new tools can improve the characterization of the spectrum of bacterial and viral infections and optimize the use of antibiotics in children. IMPACT: Transcript host RNA signatures may allow to better characterize the spectrum of viral, bacterial, and inflammatory illnesses in febrile children and can be used with traditional diagnostic methods to determine if and when to start antibiotic therapy. This is the first review on the use of transcript RNA signatures in febrile children to distinguish viral from bacterial infections. Our review identified a wide variability of target populations and gold standards used to define sepsis and SBIs, limiting the generalization of our findings.

Electronic Sensing Platform (ESP) Based on Open-Gate Junction Field-Effect Transistor (OG-JFET) for Life Science Applications: Design, Modeling and Experimental Results

This paper presents a new field-effect sensor called open-gate junction gate field-effect transistor (OG-JFET) for biosensing applications. The OG-JFET consists of a p-type channel on top of an n-type layer in which the p-type serves as the sensing conductive layer between two ohmic contacted sources and drain electrodes. The structure is novel as it is based on a junction field-effect transistor with a subtle difference in that the top gate (n-type contact) has been removed to open the space for introducing the biomaterial and solution. The channel can be controlled through a back gate, enabling the sensor's operation without a bulky electrode inside the solution. In this research, in order to demonstrate the sensor's functionality for chemical and biosensing, we tested OG-JFET with varying pH solutions, cell adhesion (human oral neutrophils), human exhalation, and DNA molecules. Moreover, the sensor was simulated with COMSOL Multiphysics to gain insight into the sensor operation and its ion-sensitive capability. The complete simulation procedures and the physics of pH modeling is presented here, being numerically solved in COMSOL Multiphysics software. The outcome of the current study puts forward OG-JFET as a new platform for biosensing applications.

Chemically Induced pH Perturbations for Analyzing Biological Barriers Using Ion-Sensitive Field-Effect Transistors

Potentiometric pH measurements have long been used for the bioanalysis of biofluids, tissues, and cells. A glass pH electrode and ion-sensitive field-effect transistor (ISFET) can measure the time course of pH changes in a microenvironment as a result of physiological and biological activities. However, the signal interpretation of passive pH sensing is difficult because many biological activities influence the spatiotemporal distribution of pH in the microenvironment. Moreover, time course measurement suffers from stability because of gradual drifts in signaling. To address these issues, an active method of pH sensing was developed for the analysis of the cell barrier in vitro. The microenvironmental pH is temporarily perturbed by introducing a low concentration of weak acid (NH₄⁺) or base (CH₃COO⁻) to cells cultured on the gate insulator of ISFET using a superfusion system. Considering the pH perturbation originates from the semi-permeability of lipid bilayer plasma membranes, induced proton dynamics are used for analyzing the biomembrane barriers against ions and hydrated species following interaction with exogenous reagents. The unique feature of the method is the sensitivity to the formation of transmembrane pores as small as a proton (H⁺), enabling the analysis of cell–nanomaterial interactions at the molecular level. The new modality of cell analysis using ISFET is expected to be applied to nanomedicine, drug screening, and tissue engineering.

Defect Engineering of Graphene to Modulate pH Response of Graphene Devices

Graphene-based pH sensors are a robust, durable, sensitive, and scalable approach for the sensitive detection of pH in various environments. However, the mechanisms through which graphene responds to pH variations are not well-understood yet. This study provides a new look into the surface science of graphene-based pH sensors to address the existing gaps and inconsistencies among the literature concerning sensing response, the role of defects, and surface/solution interactions. Herein, we demonstrate the dependence of the sensing response on the defect density level of graphene, measured by Raman spectroscopy. At the crossover point (I_D/I_G = 0.35), two countervailing mechanisms balance each other out, separating two regions where either a surface defect induced (negative slope) or a double layer induced (positive slope) response dominates. For ratios above 0.35, the pH-dependent induction of charges at surface functional groups (both pH-sensitive and nonsensitive groups) dominates the device response. Below a ratio of 0.35, the response is dominated by the modulation of charge carriers in the graphene due to the electric double layer formed from the interaction between the graphene surface and the electrolyte solution. Selective functionalization of the surface was utilized to uncover the dominant acid-base interactions of carboxyl and amine groups at low pH while hydroxyl groups control the high pH range sensitivity. The overall pH-sensing characteristics of the graphene will be determined by the balance of these two mechanisms.

Portable and Label-Free Quantitative Loop-Mediated Isothermal Amplification (LF-qLamp) for Reliable COVID-19 Diagnostics in Three Minutes of Reaction Time: Arduino-Based Detection System Assisted by a pH Microelectrode

Loop-mediated isothermal amplification (LAMP) has been recently studied as an alternative method for cost-effective diagnostics in the context of the current COVID-19 pandemic. Recent reports document that LAMP-based diagnostic methods have a comparable sensitivity and specificity to that of RT-qPCR. We report the use of a portable Arduino-based LAMP-based amplification system assisted by pH microelectrodes for the accurate and reliable diagnosis of SARS-CoV-2 during the first 3 min of the amplification reaction. We show that this simple system enables a straightforward discrimination between samples containing or not containing artificial SARS-CoV-2 genetic material in the range of 10 to 10,000 copies per 50 µL of reaction mix. We also spiked saliva samples with SARS-CoV-2 synthetic material and corroborated that the LAMP reaction can be successfully monitored in real time using microelectrodes in saliva samples as well. These results may have profound implications for the design of real-time and portable quantitative systems for the reliable detection of viral pathogens including SARS-CoV-2.

Iridium Oxide Enabled Sensors Applications

There have been numerous studies applying iridium oxides in different applications to explore their proton-change-based reactions since the 1980s. Iridium oxide can be fabricated directly by applying electrodeposition, sputter-coating method, or oxidation of iridium wire. Generally, there have been currently two approaches in applying iridium oxide to enable its sensing applications. One was to improve or create different electrolytes with (non-)electrodeposition method for better performance of Nernst Constant with the temperature-related system. The mechanism behind the scenes were summarized herein. The other was to change the structure of iridium oxide through different kinds of templates such as photolithography patterns, or template-assisted direct growth methods, etc. to improve the sensing performance. The detection targets varied widely from intracellular cell pH, glucose in an artificial sample or actual urine sample, and the hydrogen peroxide, glutamate or organophosphate pesticides, metal-ions, etc. This review paper has focused on the mechanism of electrodeposition of iridium oxide in aqueous conditions and the sensing applications towards different biomolecules compounds. Finally, we summarize future trends on Iridium oxide based sensing and predict future work that could be further explored.

An integrated E-Tube cap for sample preparation, isothermal amplification and label-free electrochemical detection of DNA

A simple, disposable, and integrated electronic-tube cap (E-tube cap) for DNA detection at the point-of-care was designed, fabricated, and tested. The E-tube cap contains a 3D printed electrode substrate for DNA extraction and label-free pH sensing detection. One Flinders Technology Associates (Whatman FTA) membrane was incorporated into the 3D printed electrode substrate for the isolation, concentration, and purification of DNA. The E-tube cap with captured DNA by the membrane was inserted directly into a reaction tube for loop-mediated isothermal amplification (LAMP). The isothermal amplification process was monitored in real-time by a 3D printed electrochemical electrode coated with pH-sensitive material (carbon/iridium oxide layer). The pH sensing electrode showed an excellent linear response within the pH range of 6-9 with a slope of -31.32 ± 0.5 mV/pH at room temperature. The utility of the integrated E-tube cap was demonstrated by detecting the presence of lambda DNA spiked in saliva samples with a sensitivity of 100 copies per mL sample within 30 min. Such a simple, rapid, and affordable diagnostic device is particularly suitable for point-of-care molecular diagnostics of infectious diseases.

Isothermal amplifications - a comprehensive review on current methods

The introduction of nucleic acid amplification techniques has revolutionized the field of medical diagnostics in the last decade. The advent of PCR catalyzed the increasing application of DNA, not just for molecular cloning but also for molecular based diagnostics. Since the introduction of PCR, a deeper understanding of molecular mechanisms and enzymes involved in DNA/RNA replication has spurred the development of novel methods devoid of temperature cycling. Isothermal amplification methods have since been introduced utilizing different mechanisms, enzymes, and conditions. The ease with which isothermal amplification methods have allowed nucleic acid amplification to be carried out has had a profound impact on the way molecular diagnostics are being designed after the turn of the millennium. With all the advantages isothermal amplification brings, the issues or complications surrounding each method are heterogeneous making it difficult to identify the best approach for an end-user. This review pays special attention to the various isothermal amplification methods by classifying them based on the mechanistic characteristics which include reaction formats, amplification information, promoter, strand break, and refolding mechanisms. We would also compare the efficiencies and usefulness of each method while highlighting the potential applications and detection methods involved. This review will serve as an overall outlook on the journey and development of isothermal amplification methods as a whole.

An ISFET Microarray Sensor System for Detecting the DNA Base Pairing

Deoxyribonucleic acid (DNA) sequencing technology provides important data for the disclosure of genetic information and plays an important role in gene diagnosis and gene therapy. Conventional sequencing devices are expensive and require large and bulky optical structures and additional fluorescent labeling steps. Sequencing equipment based on a semiconductor chip has the advantages of fast sequencing speed, low cost and small size. The detection of DNA base pairing is the most important step in gene sequencing. In this study, a large-scale ion-sensitive field-effect transistor (ISFET) array chip with more than 13 million sensitive units is successfully designed for detecting the DNA base pairing. DNA base pairing is successfully detected by the sensor system, which includes the ISFET microarray chip, microfluidic system, and test platform. The chip achieves a high resolution of at least 0.5 mV, thus enabling the recognition of the change of 0.01 pH value. This complementary metal-oxide semiconductor (CMOS) compatible and cost-efficient sensor array chip, together with other specially designed components, can form a complete DNA sequencing system with potential application in the molecular biology fields.

Detection of carbapenemase producing enterobacteria using an ion sensitive field effect transistor sensor

The timely and accurate detection of carbapenemase-producing Enterobacterales (CPE) is imperative to manage this worldwide problem in an effective fashion. Herein we addressed the question of whether the protons produced during imipenem hydrolysis could be detected using an ion sensitive field effect transistor (ISFET). Application of the methodology on enzyme preparations showed that the sensor is able to detect carbapenemases of the NDM, IMP, KPC and NMC-A types at low nanomolar concentrations while VIM and OXA-48 responded at levels above 100 nM. Similar results were obtained when CPE cell suspensions were tested; NDM, IMP, NMC-A and KPC producers caused fast reductions of the output potential. Reduction rates with VIM-type and especially OXA-48 producing strains were significantly lower. Based on results with selected CPEs and carbapenemase-negative enterobacteria, a threshold of 10 mV drop at 30 min was set. Applying this threshold, the method exhibited 100% sensitivity for NDM, IMP and KPC and 77.3% for VIM producers. The OXA-48-positive strains failed to pass the detection threshold. A wide variety of carbapenemase-negative control strains were all classified as negative (100% specificity). In conclusion, an ISFET-based approach may have the potential to be routinely used for non OXA-48-like CPE detection in the clinical laboratory.

Detection of Multiple Breast Cancer ESR1 Mutations on an ISFET Based Lab-on-Chip Platform

ESR1 mutations are important biomarkers in metastatic breast cancer. Specifically, p.E380Q and p.Y537S mutations arise in response to hormonal therapies given to patients with hormone receptor positive (HR+) breast cancer (BC). This paper demonstrates the efficacy of an ISFET based CMOS integrated Lab-on-Chip (LoC) system, coupled with variant-specific isothermal amplification chemistries, for detection and discrimination of wild type (WT) from mutant (MT) copies of the ESR1 gene. Hormonal resistant cancers often lead to increased chances of metastatic disease which leads to high mortality rates, especially in low-income regions and areas with low healthcare coverage. Design and optimization of bespoke primers was carried out and tested on a qPCR instrument and then benchmarked versus the LoC platform. Assays for detection of p.Y537S and p.E380Q were developed and tested on the LoC platform, achieving amplification in under 25 minutes and sensitivity of down to 1000 copies of DNA per reaction for both target assays. The LoC system hereby presented, is cheaper and smaller than other standard industry equivalent technologies such as qPCR and sequencing. The LoC platform proposed, has the potential to be used at a breast cancer point-of-care testing setting, offering mutational tracking of circulating tumour DNA in liquid biopsies to assist patient stratification and metastatic monitoring.

Silicene Quantum Capacitance Dependent Frequency Readout to a Label-Free Detection of DNA Hybridization- A Simulation Analysis

The use of deoxyribonucleic acid (DNA) hybridization to detect disease-related gene expression is a valuable diagnostic tool. An ion-sensitive field-effect transistor (ISFET) with a graphene layer has been utilized for detecting DNA hybridization. Silicene is a two-dimensional silicon allotrope with structural properties similar to graphene. Thus, it has recently experienced intensive scientific research interest due to its unique electrical, mechanical, and sensing characteristics. In this paper, we proposed an ISFET structure with silicene and electrolyte layers for the label-free detection of DNA hybridization. When DNA hybridization occurs, it changes the ion concentration in the surface layer of the silicene and the pH level of the electrolyte solution. The process also changes the quantum capacitance of the silicene layer and the electrical properties of the ISFET device. The quantum capacitance and the corresponding resonant frequency readout of the silicene and graphene are compared. The performance evaluation found that the changes in quantum capacitance, resonant frequency, and tuning ratio indicate that the sensitivity of silicene is much more effective than graphene.

An Optical and Temperature Assisted CMOS ISFET Sensor Array for Robust E. Coli Detection

Both bacterial viability and concentration are significant metrics for bacterial detection. Existing miniaturized and cost-effective single-mode sensor, pH or optical, can only be skilled at detecting single information viability or concentration. This paper presents an inverter-based CMOS ion-sensitive-field-effect-transistor (ISFET) sensor array, featuring bacterial pH detection which is an indicator of viability. The proposed design realizes pH detection using the native passivation layer of CMOS process as a sensing layer and configuring an inverter-based front-end as a capacitive feedback amplifier. This sensor array is assisted by temperature sensing and optical detection which reveals bacterial concentration. The optical detection is enabled using the leakage current of a reset switch as a response to a light source. While in reset mode, the inverter-based amplifier works as a temperature sensor that could help to reduce temperature influences on pH and optical detection. All the functionalities are realized using one single inverter-based amplifier, resulting in a compact pixel structure and largely relaxed design complexity for the sensor system. Fabricated in 0.18 μm standard CMOS process, the proposed CMOS sensor array system achieves an amplified pH sensitivity of 221 mV/pH, an improved sensor resolution of 0.03 pH through systematic noise optimization, a linear optical response, and a maximum temperature error of 0.69 ^°C. The sensing capabilities of the proposed design are demonstrated through on-chip Escherichia coli (E. coli) detection. This study may be extended to a rapid and cost-effective platform that renders multiple information of bacterial samples.

Hairpin DNA-Mediated isothermal amplification (HDMIA) techniques for nucleic acid testing

Nucleic acid detection is of great importance in a variety of areas, from life science and clinical diagnosis to environmental monitoring and food safety. Unfortunately, nucleic acid targets are always found in trace amounts and their response signals are difficult to be detected. Amplification mechanisms are then practically needed to either duplicate nucleic acid targets or enhance the detection signals. Polymerase chain reaction (PCR) is one of the most popular and powerful techniques for nucleic acid analysis. But the requirement of costly devices for precise thermo-cycling procedures in PCR has severely hampered the wide applications of PCR. Fortunately, isothermal molecular reactions have emerged as promising alternatives. The past decade has witnessed significant progress in the research of isothermal molecular reactions utilizing hairpin DNA probes (HDPs). Based on the nucleic acid strand interaction mechanisms, the hairpin DNA-mediated isothermal amplification (HDMIA) techniques can be mainly divided into three categories: strand assembly reactions, strand decomposition reactions, and strand creation reactions. In this review, we introduce the basics of HDMIA methods, including the sensing principles, the basic and advanced designs, and their wide applications, especially those benefiting from the utilization of G-quadruplexes and nanomaterials during the past decade. We also discuss the current challenges encountered, highlight the potential solutions, and point out the possible future directions in this prosperous research area.

Stem-loop-primer assisted isothermal amplification enabling high-specific and ultrasensitive nucleic acid detection

It is highly desired to perform accurate and rapid nucleic acid detections for disease diagnosis at resource-limited setting, such as small clinics, remote areas and home. However, the challenges in sample handling, expensive equipment and complicated operation make canonical polymerase chain reaction (PCR) impossible to run the point-of-care testing (POCT). Herein we report a novel nucleic acid detection method, named stem-loop-primer assisted isothermal amplification (SPA), which specifically and sensitively amplifies target nucleic acid by using Bst DNA polymerase, a pair of canonical PCR primers and their stem-loop derivatives. The stem-loop-primers are easily designed by adding a stem-loop sequence to the canonical PCR primers at 5'-ends. In contrast to loop-mediated isothermal amplification (LAMP), which is a widespread isothermal amplification technology, our SPA is more specific and convenient to design and run. Further, we have demonstrated that SPA can specifically detect type 16, 18, 52 and 58 Human Papilloma viruses (HPV) in cervical samples, suggesting its specificity and robustness for nucleic acid detection. Moreover, pH indicator based colorimetric SPA was developed, which offered 100% accuracy for HPV16 detection in cervical samples, thereby demonstrating its great potential for POCT nucleic acid testing.

Aptasensor for Quantification of Leptin Through PCR Amplification of Short DNA-Aptamers

Protein quantification is traditionally performed through enzyme-linked immunosorbent assay (ELISA), which involves long preparation times. To overcome this, new approaches use aptamers as an alternative to antibodies. In this paper, we present a new approach to quantify proteins with short DNA aptamers through polymerase chain reaction (PCR) resulting in shorter protocol times with comparatively improved limits of detection. The proposed method includes a novel way to quantify both the target protein and the corresponding short DNA-aptamers simultaneously, which also allows us to fully characterize the performance of aptasensors. Human leptin is used as a target protein to validate this technique, because it is considered an important biomarker for obesity-related studies. In our experiments, we achieved the lowest limit of detection of 100 pg/mL within less than 2 h, a limit affected by the dissociation constant of the leptin aptamer, which could be improved by selecting a more specific aptamer. Because of the simple and inexpensive approach, this technique can be employed for Lab-On-Chip implementations and for rapid "on-site" quantification of proteins.

The Loop-Mediated Isothermal Amplification Technique in Periodontal Diagnostics: A Systematic Review

The course of periodontal disease is affected by many factors; however, the most significant are the dysbiotic microflora, showing different pathogenicity levels. Rapid colonization in the subgingival environment can radically change the clinical state of the periodontium. This systematic review aims to present an innovative technique of loop-mediated isothermal amplification for rapid panel identification of bacteria in periodontal diseases. The decisive advantage of the loop-mediated isothermal amplification (LAMP) technique in relation to molecular methods based on the identification of nucleic acids (such as polymerase chain reaction (PCR or qPCR) is the ability to determine more pathogens simultaneously, as well as with higher sensitivity. In comparison with classical microbiological seeding techniques, the use of the LAMP method shortens a few days waiting time to a few minutes, reducing the time necessary to identify the species and determine the number of microorganisms. The LAMP technology requires only a small hardware base; hence it is possible to use it in outpatient settings. The developed technique provides the possibility of almost immediate assessment of periodontal status and, above all, risk assessment of complications during the treatment (uncontrolled spread of inflammation), which can certainly be of key importance in clinical work.