Distance-based paper/PMMA integrated ELISA-chip for quantitative detection of immunoglobulin G

Recent advancements in the sensors for food analysis to detect gluten: A mini-review [2019-2023]

People with celiac disease or gluten sensitivity may experience an immune reaction to the protein called gluten, which is present in wheat, barley, and rye. A strict gluten-free diet is the sole cure for these ailments. There are chances of food fraud about the claim of being gluten-free food items. As a result, there is a rising need for trustworthy and precise ways to identify gluten. There are many methods to detect gluten in food samples viz., enzyme-linked immunosorbent assay 1 Surface plasmon resonance (SPR), Electrochemical sensors, Fluorescence-based sensors, etc. The use of sensors is one of the most promising methods for gluten detection. For detecting gluten, a variety of sensors, including optical, electrochemical, and biosensors, have been developed with different limits of detection and sensitivity. The present review reports the recent advancements (2019-2023) in the development of sensors for gluten detection in food. We may conclude that sensitivity and limit of detection are not related to the type of sensor used (aptamer or antibody-based), however, there are advancements, with the year, on the simplicity of the material used like paper-based sensors and paradigm shift to reagent free sensors by the spectral analysis. Also, recent work shows the potential of IoT-based studies for gluten detection.

Quantitative and equipment-free paper-based agglutination assay of bacterial cells

Background: point-of-care (POC) tests are useful for bedside/home applications, emergencies, frequent follow-ups, and resource-limited areas. Limited quantitative and equipment-free POC assays have been reported. This study aims to develop, validate, and apply a simple, quantitative, paper-based POC assay. Methods: wax-channeled paper treated with specific anti-Brucella and anti-Salmonella antibodies was used for distance-based chromatographic elution of stained bacterial cell agglutinations. Results: a qualitative paper-based agglutination POC test was developed using color intensity, tail appearance, and "+/-" signs that clearly distinguish the positive and negative results. The optimization of the test for paper type, microfluidic channel design, antibody and bacterial cell concentrations, and elution methods was carried out. Quantitative assay transformation was successfully developed using the color intensity of the original reaction zone, intensity of elution tail, and distance-based migration that correspond to bacterial agglutination size. The migration distance of eluted bacterial agglutination bands corresponds to the target concentration with good linearity and minimal variability. Reporting of colored band migration with numbers using microfluidic patterns was used to enhance non-technical end-user applications. A distance-based POC assay prototype was then successfully used for the accurate detection of known and unknown samples in comparison with standard assays. Conclusions: the migration distance of an eluted stained bacterial agglutination correlated with anti-bacterial antibody concentrations. A simple, cheap, quantitative, and equipment-free paper-based POC assay of bacterial cell agglutination was developed. This test can be used for simple "+/-" results, thermometer-like quantification, or text reporting with numbers corresponding to target concentrations. The assay has extended applications to different human disease biomarkers.

Progress in Procalcitonin Detection Based on Immunoassay

Procalcitonin (PCT) serves as a crucial biomarker utilized in diverse clinical contexts, including sepsis diagnosis and emergency departments. Its applications extend to identifying pathogens, assessing infection severity, guiding drug administration, and implementing theranostic strategies. However, current clinical deployed methods cannot meet the needs for accurate or real-time quantitative monitoring of PCT. This review aims to introduce these emerging PCT immunoassay technologies, focusing on analyzing their advantages in improving detection performances, such as easy operation and high precision. The fundamental principles and characteristics of state-of-the-art methods are first introduced, including chemiluminescence, immunofluorescence, latex-enhanced turbidity, enzyme-linked immunosorbent, colloidal gold immunochromatography, and radioimmunoassay. Then, improved methods using new materials and new technologies are briefly described, for instance, the combination with responsive nanomaterials, Raman spectroscopy, and digital microfluidics. Finally, the detection performance parameters of these methods and the clinical importance of PCT detection are also discussed.

Investigation of geometry-dependent sensing characteristics of microfluidic for single-cell 3D localization

Flow cytometry-based measurement techniques have been widely used for single-cell characterizations, such as impedance, size, and dielectric properties. However, in the measurement process, the reliability of the output measurement signal directly affects the ability of the microsystem to judge the characteristics of single cells. Here, we designed a multiple nonparallel electrode structure for single-cell 3D localization. The performance of the structures was studied by analyzing the changes in electric field strength and the output differential current. The effects of microchannel height, sensing electrode distance, electrode inclination angle, and electrode width on output signals are investigated by analyzing the current change and electric field strength of single cells passing from the center of the microchannel. The numerical simulation results indicate that, when the microchannel height is 20 µm, the distance of the sensing electrodes is 100 µm, the inclination angle is 30°, the electrode width is 20 µm, and the optimal signal quality can be obtained. Reducing the height of the flow channel and shortening the sensing electrode spacing can significantly improve the signal amplitude. When the channel height is 20 µm, the signal intensity increases by 80% than that of 30 µm. The signal intensity of induced current with the sensing electrode spacing of 100 µm is 42% higher than that with the spacing of 120 µm. We analyzed the presence of multiple independent cells and adherent cells in the detection area and demonstrated through simulation that the signal changes caused by multi-cells can be superimposed by multiple single-cell signals. The induced current signal intensity of the same volume of cells with an ellipticity of 1 is 49% lower than that of cells with an ellipticity of 4. Based on the numerical investigation, we expect that the optimal geometry structure design will aid in the development of better performance signal cell impedance cytometry microsystems.

Sample-to-answer sensing technologies for nucleic acid preparation and detection in the field

Efficient sample preparation and accurate disease diagnosis under field conditions are of great importance for the early intervention of diseases in humans, animals, and plants. However, in-field preparation of high-quality nucleic acids from various specimens for downstream analyses, such as amplification and sequencing, is challenging. Thus, developing and adapting sample lysis and nucleic acid extraction protocols suitable for portable formats have drawn significant attention. Similarly, various nucleic acid amplification techniques and detection methods have also been explored. Combining these functions in an integrated platform has resulted in emergent sample-to-answer sensing systems that allow effective disease detection and analyses outside a laboratory. Such devices have a vast potential to improve healthcare in resource-limited settings, low-cost and distributed surveillance of diseases in food and agriculture industries, environmental monitoring, and defense against biological warfare and terrorism. This paper reviews recent advances in portable sample preparation technologies and facile detection methods that have been / or could be adopted into novel sample-to-answer devices. In addition, recent developments and challenges of commercial kits and devices targeting on-site diagnosis of various plant diseases are discussed.

A 3D paper microfluidic device for enzyme-linked assays: Application to DNA analysis

A paper microfluidic device capable of conducting enzyme-linked assays is presented: a microfluidic enzyme-linked paper analytical device (μEL-PAD). The system exploits a wash-free sandwich coupling to form beads/analyte/enzyme complexes, which are subsequently added to the vertical flow device composed of wax-printed paper, waxed nitrocellulose membrane and absorbent/barrier layers. The nitrocellulose retains the bead complexes without disrupting the flow, enabling for an efficient washing step. The entrapped complexes then interact with the chromogenic substrate stored on the detection paper, generating a color change on it, quantified with an open-source smartphone software. This is a universal paper-based technology suitable for high-sensitivity quantification of many analytes, such as proteins or nucleic acids, with different enzyme-linked formats. Here, the potential of the μEL-PAD is demonstrated to detect DNA from Staphylococcus epidermidis. After generation of isothermally amplified genomic DNA from bacteria, Biotin/FITC-labeled products were analyzed with the μEL-PAD, exploiting streptavidin-coated beads and antiFITC-horseradish peroxidase. The μEL-PAD achieved a limit of detection (LOD) and quantification <10 genome copies/μL, these being at least 70- and 1000-fold lower, respectively, than a traditional lateral flow assay (LFA) exploiting immobilized streptavidin and antiFITC-gold nanoparticles. It is envisaged that the device will be a good option for low-cost, simple, quantitative, and sensitive paper-based point-of-care testing.

A versatile and automated microfluidic platform for a quantitative magnetic bead based protocol: application to gluten detection

A microfluidic platform for the integration of multi-step biological assays has been developed. The presented system is a unique instrument compatible with microfluidic chips for various applications based on bead manipulation. Two examples of microfluidic cartridges are presented here. The first one contains two rows of eight chambers (40 and 80 μL), six reagent inlets, eight testing solution (calibrators and samples) inlets and eight outlets to reproduce precisely each step of a biological assay. This configuration is versatile enough to integrate many different biological assays and save a lot of development time. The second architecture is dedicated to one specific protocol and is completely automated from the standard and sample dilutions to the optical detection. Linear dilutions have been integrated to prepare automatically a range of standard concentrations and outlets have been modified for integrated colorimetric detection. The technology uses pneumatically collapsible chambers to perform all the fluidic operations for a fully automated protocol such as volume calibrations, fluid transport, mixing, and washing steps. A programmable instrument with a software interface has been developed to adapt rapidly a protocol to this cartridge. As an example, these new microfluidic cartridges have been used to successfully perform an immunoassay for gluten detection in the dynamic range of 10-30 ppm with good sensitivity (2 ppm) and specificity.

Magnetofluid-Integrated Multicolor Immunochip for Visual Analysis of Neutralizing Antibodies to SARS-CoV-2 Variants

The global spread of SARS-CoV-2 virus has severely affected human health, life, and work. Vaccine immunization is considered to be an effective means to protect the body from infection. Therefore, timely analysis of the antibody level is helpful to identify people with low immune response or attenuated antibodies so as to carry out targeted and precise vaccine booster immunization. Herein, we develop a magnetofluid-integrated multicolor immunochip, as a sample-to-answer system in a fully enclosed space, for visual analysis of neutralizing antibodies of SARS-CoV-2. Generally, this chip adopts an innovative three-dimensional two-phase system that utilizes mineral oil to block the connection between reagent wells in the vertical direction and provides a wide interface for rapid and nondestructive shuttle of magnetic beads during the immunoassay. In order to obtain visualized signal output, gold nanorods with a size-dependent color effect are used as the colorful chromogenic substrates for evaluation of the antibody level. Using this chip, the neutralizing antibodies were successfully detected in vaccine-immunized volunteers with 83.3% sensitivity and 100% specificity. Furthermore, changes in antibody levels of the same individual over time were also reflected by the multicolor assay. Overall, benefiting from simple operation, airtight safety, and nonrequirement of external equipment, this platform can provide a new point-of-care testing strategy for alleviating the shortage of medical resources and promoting epidemic control in underdeveloped areas.

Recent Advances and Applications in Paper-Based Devices for Point-of-Care Testing

Point-of-care testing (POCT), as a portable and user-friendly technology, can obtain accurate test results immediately at the sampling point. Nowadays, microfluidic paper-based analysis devices (μPads) have attracted the eye of the public and accelerated the development of POCT. A variety of detection methods are combined with μPads to realize precise, rapid and sensitive POCT. This article mainly introduced the development of electrochemistry and optical detection methods on μPads for POCT and their applications on disease analysis, environmental monitoring and food control in the past 5 years. Finally, the challenges and future development prospects of μPads for POCT were discussed.

Colorimetric monitoring of serum dopamine with promotion activity of gold nanocluster-based nanozymes

Over the past few decades, metal nanoparticles have been actively investigated as enzyme mimetic nanomaterials. However, the catalytic activity of gold nanocluster (AuNCs)-based nanozymes is relatively low. It is still a great challenge to improve the enzyme-mimic catalytic property of AuNCs, and to explore the roles of the charges on the surface of the nanozymes and reactive oxygen species in the catalytic reaction systems. This study describes a simple synthesis of AuNCs capped with papain (P@AuNCs). The as-prepared P@AuNCs exhibited an efficient peroxidase-mimic ability via the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide. Interestingly, the negatively charged dopamine was able to trigger the aggregration of the positively charged P@AuNCs and reactive oxygen species generated in the oxidation process, resulting in a remarkable catalytic activity promotion of P@AuNCs. Based on this principle, a protocol for the highly selective and sensitive monitoring of dopamine has been constructed with the colour change from pale blue to deep blue. The ultraviolet-visible absorbance of P@AuNCs-TMB at the wavelength of 650 nm showed a good linear relationship with the dopamine concentration ranging from 2.0 μM to 25.0 μM (R² = 0.990). The limit of detection was 0.8 μM. Furthermore, dopamine was monitored in a drug metabolic process following the abdominal injection in rats using the proposed colorimetric assay. It offers an easy approach for the fabrication of AuNCs-based nanozymes with an improved catalytic activity, and provides a great potential application in the measuring of real serum drugs.

Microfluidic colorimetric detection platform with sliding hybrid PMMA/paper microchip for human urine and blood sample analysis

A microfluidic colorimetric detection (MCD) platform consisting of a sliding hybrid PMMA/paper microchip and a smart analysis system is proposed for the convenient, low-cost and rapid analysis of human urine and whole blood samples. The sliding PMMA/paper microchip comprises a PMMA microfluidic chip for sample injection and transportation, a paper strip for sample filtration (urine) or separation (blood), and a sealed paper-chip detection zone for sample reaction and detection. In the proposed device, the paper-chip is coated with bicinchoninic acid (BCA) and biuret reagent and is then assembled into the PMMA microchip and packaged in aluminum housing. In the detection process, the PMMA/paper microchip is slid partially out of the housing, and 2 μL of sample (urine or whole blood) is dripped onto the sample injection zone. The chip is then slid back into the housing and the sample is filtered/separated by the paper strip and transferred under the effects of capillary action to the sealed paper-chip detection zone. The housing is inserted into the color analysis system and heated at 45 °C for 5 min to produce a purple-colored reaction complex. The complex is imaged using a CCD camera and the RGB color intensity of the image is then analyzed using a smartphone to determine the total protein (TP) concentration of the sample. The effectiveness of the proposed method is demonstrated using TP control samples with known concentrations in the range of 0.03-5.0 g/dL. The detection results obtained for 50 human urine samples obtained from random volunteers are shown to be consistent with those obtained from a conventional hospital analysis system (R² = 0.992). Moreover, the detection results obtained for the albumin (ALB) and creatine (CRE) concentrations of 50 whole blood samples are also shown to be in good agreement with the results obtained from the hospital analysis system (R² = 0.982 and 0.988, respectively).

Selective Molecular Recognition of Low Density Lipoprotein Based on β-Cyclodextrin Coated Electrochemical Biosensor

The excess of low-density lipoprotein (LDL) strongly promotes the accumulation of cholesterol on the arterial wall, which can easily lead to the atherosclerotic cardiovascular diseases (ACDs). It is a challenge on how to recognize and quantify the LDL with a simple and sensitive analytical technology. Herein, β-cyclodextrins (β-CDs), acting as molecular receptors, can bind with LDL to form stable inclusion complexes via the multiple interactions, including electrostatic, van der Waals forces, hydrogen bonding and hydrophobic interactions. With the combination of gold nanoparticles (Au NPs) and β-CDs, we developed an electrochemical sensor providing an excellent molecular recognition and sensing performance towards LDL detection. The LDL dynamic adsorption behavior on the surface of the β-CD-Au electrode was explored by electrochemical impedance spectroscopy (EIS), displaying that the electron-transfer resistance (Ret) values were proportional to the LDL (positively charged apolipoprotein B-100) concentrations. The β-CD-Au modified sensor exhibited a high selectivity and sensitivity (978 kΩ·µM⁻¹) toward LDL, especially in ultra-low concentrations compared with the common interferers HDL and HSA. Due to its excellent molecular recognition performance, β-CD-Au can be used as a sensing material to monitor LDL in human blood for preventing ACDs in the future.

Microfluidic impedance cytometry for single-cell sensing: Review on electrode configurations

Single-cell analysis has gained considerable attention for disease diagnosis, drug screening, and differentiation monitoring. Compared to the well-established flow cytometry, which uses fluorescent-labeled antibodies, microfluidic impedance cytometry (MIC) offers a simple, label-free, and noninvasive method for counting, classifying, and monitoring cells. Superior features including a small footprint, low reagent consumption, and ease of use have also been reported. The MIC device detects changes in the impedance signal caused by cells passing through the sensing/electric field zone, which can extract information regarding the size, shape, and dielectric properties of these cells. According to recent studies, electrode configuration has a remarkable effect on detection accuracy, sensitivity, and throughput. With the improvement in microfabrication technology, various electrode configurations have been reported for improving detection accuracy and throughput. However, the various electrode configurations of MIC devices have not been reviewed. In this review, the theoretical background of the impedance technique for single-cell analysis is introduced. Then, two-dimensional, three-dimensional, and liquid electrode configurations are discussed separately; their sensing mechanisms, fabrication processes, advantages, disadvantages, and applications are also described in detail. Finally, the current limitations and future perspectives of these electrode configurations are summarized. The main aim of this review is to offer a guide for researchers on the ongoing advancement in electrode configuration designs.

An electricity- and instrument-free infectious disease sensor based on a 3D origami paper-based analytical device

Infectious diseases cause millions of deaths annually in the developing world. Recently, microfluidic paper-based analytical devices (μPADs) have been developed to diagnose such diseases, as these tests are low cost, biocompatible, and simple to fabricate. However, current μPADs are difficult to use in resource-limited areas due to their reliance on external instrumentation to measure and analyze the test results. In this work, we propose an electricity and external instrumentation-free μPAD sensor based on the colorimetric enzyme-linked immunosorbent assay (ELISA) for the diagnosis of infectious disease (3D-tPADs). Designed based on the principle of origami, the proposed μPAD enables the sequential steps of the colorimetric ELISA test to be completed in just ∼10 min. In addition, in order to obtain an accurate ELISA result without using any instrument, we have integrated an electricity-free "timer" within the μPAD that can be controlled by the buffer viscosity and fluid path volume to indicate the appropriate times for washing and color development steps, which can avoid false positive or false negative results caused by an extended or shortened amount of washing and development times. Due to the low background noise and high positive signal intensity of the μPAD, positive and negative detection results can be distinguished by just the naked eye. Furthermore, the ELISA result can be semi-quantified by comparing the results shown on the μPAD with a color chart diagram with a detection limit of HIV type 1(HIV-1) p24 antigen as low as 0.03 ng mL-1. These results demonstrate the proposed sensor can perform infectious disease diagnosis without external instrumentation or electricity, extending the application of the μPAD test for on-site detection and use in resource-limited settings.

Clinical Therapy of Metastatic Spinal Tumors

Metastatic spinal tumors (MST) have high rates of morbidity and mortality. MST can destroy the vertebral body or compress the nerve roots, resulting in an increased risk of pathological fractures and intractable pain. Here, we elaborately reviewed the currently available therapeutic options for MST according to the following four aspects: surgical management, minimally invasive therapy (MIT), radiation therapy, and systemic therapy. In particular, these aspects were classified and introduced to show their developmental process, clinical effects, advantages, and current limitations. Furthermore, with the improvement of treatment concepts and techniques, we discovered the prevalent trend toward the use of radiation therapy and MIT in clinic therapies. Finally, the future directions of these treatment options were discussed. We hoped that along with future advances and study will lead to the improvement of living standard and present status of treatment in patients with MST.