Toward the point-of-care testing of alkaline phosphatase in human serum

This work addresses challenges of simple but reliable determination of enzyme alkaline phosphatase (ALP) in μL-sized serum samples. The single-tube assay and plate-based immunoassay were developed by using a commercial glucose test strip (GTS) to transduce analytical signal from the ALP + glucose-6-phosphate (G6P) reaction. The glucose released from G6P contributed to the flow of anodic charge Q20s through GTS. The interferences from serum matrix including those from native glucose were eliminated by devising a signal ΔQ20s = Q20s (total) - Q20s (matrix). The ΔQ20s was proportional to ALP activity within a linear range of 7.4-720 IU L-1 for assay (R2, 0.995) and 10-300 IU L-1 for immunoassay (R2, 0.983), which far exceeded a normal clinical range for ALP in adult human serum (30-150 IU L-1). Both methods required no auxiliary enzymes or labels, and were accurate (93-99 % signal recovery) and precise (RSD ≤10%). The assay was a simpler option because it required only one 20-min incubation step to determine ALP. The immunoassay involved three steps but it was still less laborious (by ∼70%) than a traditional enzyme-linked immunosorbent assay (ELISA) of ALP due to the substitution of ELISA detection antibody with GTS. The GTS-G6P-based methods bring ALP testing closer to the point-of-care locations, which is important considering the growing role of ALP as a prophylactic, therapeutic, and anti-inflammatory agent, and a marker of human diseases.

A dual-mode strategy based on β-galactosidase and target-induced DNA polymerase protection for transcription factor detection using colorimetry and a glucose meter

In this work, we report a novel dual-mode method for the highly specific and sensitive detection of transcription factors (TFs) via the integration of Klenow polymerase protection induced by target-specific recognition, cascade-signal amplification using the hybridization chain reaction (HCR) and CRISPR/Cas12a system, and dual-signal transduction mediated by β-galactosidase (β-gal) and two substrates. A dual-mode signal-sensing interface was constructed by immobilizing the oligo DNA probe (P1) tethered β-gal in a 96-well plate. A hairpin H1 with the ability to initiate HCRs was designed to contain the TF binding site. The binding between the TF and H1 protected the H1 from being extended by the Klenow fragment. After thermal denaturation, the reserved H1 launched the HCR and the HCR products activated CRISPR/Cas12a to cleave P1 and reduce the β-gal on the sensing interface, and thus the contents of the TFs and the corresponding signals mediated by the catalysis of β-gal showed a correlation. This work was the first attempt at utilizing β-gal for dual-signal transduction. It is a pioneering study to utilize the HCR-CRISPR/Cas12a system for dual-mode TF sensors. It revealed that DNA polymerase protection through the binding of TF and DNA could be applied as a new pattern to develop TF sensors.

Construction of a portable immunosensor for the sensitive detection of carbendazim in agricultural products using a personal glucose meter

Portable and sensitive detection of carbendazim (CBD) is highly desirable for food safety and environmental protection. Herein, a portable immunosensor for the sensitive detection of CBD is proposed based on alkaline phosphatase (ALP)-labeled and secondary antibody-modified gold nanoparticles (AuNPs). The quantification is based on ALP catalyzing the dephosphorylation of glucose-1-phosphate disodium salt to generate glucose, thus converting the concentration of CBD into glucose, thereby realizing the portable detection of CBD by personal glucose meter. Benefiting from signal amplification strategy that integrates the large specific surface area of AuNPs, the enzymatic reactions of terminal deoxynucleotidyl transferase and ALP, a low detection limit of 0.37 ng/mL for CBD is achieved. When this portable method is used to analyze citrus fruit, canned citrus, and cabbage, good-consistency results are obtained with the UPLC-MS/MS method. The good performance demonstrates the great potential of this portable method for CBD monitoring in resource-poor settings.

Advanced biosensors for mycotoxin detection incorporating miniaturized meters

Advanced biosensors, considered as emerging technologies, are capable of accurate, quantitative and real-time analysis for point-of-care testing (POCT) applications. Moreover, the integrating of miniaturized meters into these advanced biosensors makes them ideally appropriate for portable, sensitive and selective detection of biomolecules. Miniaturized meters including PGMs (personal glucose meters), thermometer, pressuremeter, pH meter, etc. are the most accurate devices and wide availability in the market, exhibiting a promising potential towards detection of small molecule mycotoxins. In this article, we introduce and analyze the recent advancements for sensing of mycotoxins measured by handheld meters since the first report in 2012. Furthermore, limitations and challenges for versatile meters application against mycotoxins in food matrix are highlighted. By overcoming the bottleneck problems, we believe the miniaturized meters-based biosensor platform will provide great possibilities for mycotoxins analysis and launch them to the market.

Overcoming Major Barriers to Developing Successful Sensors for Practical Applications Using Functional Nucleic Acids

For many years, numerous efforts have been focused on the development of sensitive, selective, and practical sensors for environmental monitoring, food safety, and medical diagnostic applications. However, the transition from innovative research to commercial success is relatively sparse. In this review, we identify four scientific barriers and one technical barrier to developing successful sensors for practical applications, including the lack of general methods to (a) generate receptors for a wide range of targets, (b) improve sensor selectivity to overcome interferences, (c) transduce the selective binding to different optical, electrochemical, and other signals, and (d) tune dynamic range to match thresholds of detection required for different targets; and the costly development of a new device. We then summarize solutions to overcome these barriers using sensors based on functional nucleic acids that include DNAzymes, aptamers, and aptazymes and how these sensors are coupled to widely available measurement devices to expand their capabilities and lower the barrier for their practical applications in the field and point-of-care settings.

Dual cascade isothermal amplification reaction based glucometer sensors for point-of-care diagnostics of cancer-related microRNAs

The practical use of a point-of-care (POC) device is of particular interest in performing liquid biopsies related to cancer. Herein, taking advantage of the practical convenience of a commercially available personal glucose meter (PGM), we report a convenient, low-cost and sensitive detection strategy for circulating microRNA-155 (miRNA155) in human serum. First, miRNA155 in serum triggers the catalyzed hairpin assembly (CHA) reaction, and then the CHA product is specifically captured by the peptide nucleic acid (PNA) probes attached to the surface of a 96-well plate, which in turn triggers the hybridization chain reaction (HCR), resulting in the local enrichment of invertase. Next, introduction of a substrate (sucrose) for the invertase results in the generation of glucose, which can be detected by a PGM. In this sensor, neutrally charged PNA (12 nt) is more likely to hybridize with the CHA products than with the negatively charged DNA in kinetics, which improves the detection sensitivity and specificity. Due to the synergistic isothermal amplification reaction between CHA and HCR, the sensor is able to achieve a broad dynamic range (from 1 fM to 10 nM) with a detection limit down to 0.36 fM (3 orders of magnitude lower than that without HCR) and is capable of distinguishing single-base mismatched sequences. Thus the convenient, sensitive, robust and low-cost PGM sensor makes on-site nucleic acids detection possible, suggesting its great application prospect as a promising POC device in cancer diagnostics.

DNAzyme Amplified Aptasensing Platform for Ochratoxin A Detection Using a Personal Glucose Meter

Aptamer-based sensors have emerged as a major platform for detecting small-molecular targets, because aptamers can be selected to bind these small molecules with higher affinity and selectivity than other receptors such as antibodies. However, portable, accurate, sensitive, and affordable detection of these targets remains a challenge. In this work, we developed an aptasensing platform incorporating magnetic beads and a DNAzyme for signal amplification, resulting in high sensitivity. The biosensing platform was constructed by conjugating a biotin-labeled aptamer probe of small-molecular targets such as toxins and a biotin-labeled substrate strand on magnetic beads, and the DNAzyme strand hybridized with the aptamer probe to block the substrate cleavage activity. The specific binding of the small-molecular target by the aptamer probe can replace the DNAzyme strand and then induce the hybridization between the DNAzyme strand and substrate strand, and the iterative signal amplification reaction of hydrolysis and cleavage of the substrate chain occurs in the presence of a metal ion cofactor. Using invertase to label the substrate strand, the detection of small molecules of the toxin is successfully transformed into the measurement of glucose, and the sensitive analysis of small molecules such as toxins can be realized by using the household portable glucose meter as a readout. This platform is shown to detect ochratoxin, a common toxin in food, with a linear detection range of 5 orders of magnitude, a low detection limit of 0.88 pg/mL, and good selectivity. The platform is easy to operate and can be used as a potential choice for quantitative analysis of small molecules, at home or under point-of-care settings. Moreover, by changing and designing the aptamer probe and the arm of DNAzyme strand, it can be used for the analysis of other analytes.

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

The enzyme-linked immunosorbent assay (ELISA) is one of the most commonly implemented clinical diagnostic tools for the detection and quantification of protein biomarkers. However, conventional ELISA tests require sophisticated infrastructure, expensive reagents, long assay time, and expertise for operation, which are not often easily accessible in resource-limited settings. Microfluidic ELISA-chip based point-of-care (POC) testing allows miniaturization and integration of complex functions that facilitate their usage in limited-resource settings. The current work demonstrates a simple, portable, low cost and equipment-free paper/poly(methyl methacrylate) (PMMA) integrated microfluidic ELISA-chip as a POC device with a visual distance-based readout for quantitative detection of clinical biomarkers. The integrated paper/PMMA ELISA-chip utilizes the movement of immunoassay complexes with magnetic beads by a permanent magnet in a PMMA part of the compartment. The target concentration is translated into a visual distance signal readout for quantitative detection of biomarkers in a μPAD. Because it does not require sophisticated instruments and has the added advantages of low cost, easy operation, and disposability with quantitative visual readout, the paper/PMMA ELISA-chip holds great promise for portable detection of target bioanalytes as a POC diagnostic tool in resource-limited setups.

New Uses for the Personal Glucose Meter: Detection of Nucleic Acid Biomarkers for Prostate Cancer Screening

A personal glucose meter (PGM)-based method for quantitative detection of a urinary nucleic acid biomarker in prostate cancer screening, the so-called PCA3, is reported herein. A sandwich-type genoassay is conducted on magnetic beads to collect the target from the sample by specific hybridization, making the assay appropriate for PCA3 detection in biological fluids. The success of the method hinges on the use of alkaline phosphatase (ALP) to link the amount of nucleic acid biomarker to the generation of glucose. In particular, specifically attached ALP molecules hydrolyze D-glucose-1-phosphate into D-glucose, thus enabling the amplification of the recorded signal on the personal glucose meter. The developed genoassay exhibits good sensitivity (3.3 ± 0.2 mg glucose dL-1 pM-1) for PCA3, with a dynamic range of 5 to 100 pM and a quantification limit of 5 pM. Likewise, it facilitates point-of-care testing of nucleic acid biomarkers by using off-the-shelf PGM instead of complex instrumentation involved in traditional laboratory-based tests.

Two-Dimensional Device with Light-Controlled Capability for Treatment of Cancer-Relevant Infection Diseases

Concurrent infection in cancer treatment is the leading cause of high cancer mortality that requires urgent action. Currently developed diagnostic methods are hindered by the difficulty of rapidly and reliably screening small amounts of pathogens in the blood and then release pathogens for downstream analysis, limiting the advance of cancer concurrent infection diseases diagnosis and targeted treatment. Herein, we present a near-infrared (NIR) light-responsive black phosphorus (BP)-based device that effectively captures and releases pathogen for downstream drug-resistance analysis. The aptamer-modified BP nanostructures exhibit enhanced topographical interactions and binding capabilities with pathogen, enabling highly efficient and selective capture of pathogen in serum. NIR light irradiation induces BP nanostructure to generate a local thermal effect, which regulates the three-dimensional structure of the aptamer and causes efficient release of pathogen from the substrate surface. The released pathogen is resistant to ampicillin as demonstrated by downstream genetic analysis. The design of the functionalized light-controlled device for monitoring pathogen behavior shows great potential for assisting in cancer therapy and promoting personalized healthcare.

Colorimetric aptasensor for ochratoxin A detection based on enzyme-induced gold nanoparticle aggregation

An innovative colorimetric method based on enzyme-induced gold nanoparticle aggregation was developed to detect the activity of alkaline phosphatase (ALP), and it was further applied to construct an aptasensor to monitor ochratoxin A (OTA) concentrations. In the presence of ALP, the substrate ascorbic acid 2-phosphate was hydrolyzed to generate ascorbic acid (AA). Subsequently, reduction of MnO₂ nanosheets by AA produced manganese ions, which mediated gold nanoparticle aggregation. The color of the detection solution changed from brown-red to purple to blue as the ALP concentration increased, and a detection limit of 0.05 U·L^-1 was achieved. Furthermore, this strategy was successfully utilized to devise a target-responsive aptasensor for colorimetric detection of an important mycotoxin, OTA, which causes food poisoning and has various toxic effects on humans. The proposed method offers high sensitivity with a detection limit as low as 5.0 nM together with high specificity. When applied to analyze red wine and grape juice samples, no complex sample pretreatment or bulky instruments were required. Overall, a colorimetric platform based on enzyme-induced gold nanoparticle aggregation was successfully established to improve the simplicity and sensitivity of ALP and OTA detection. This platform appears highly promising for mycotoxin-related food safety monitoring.

Translating in vitro diagnostics from centralized laboratories to point-of-care locations using commercially-available handheld meters

There is a growing demand for high-performance point-of-care (POC) diagnostic technologies where in vitro diagnostics (IVD) is fundamental for prevention, identification, and treatment of many diseases. Over the past decade, a shift of IVDs from the centralized laboratories to POC settings is emerging. In this review, we summarize recent progress in translating IVDs from centralized labs to POC settings using commercially available handheld meters. After introducing typical workflows for IVDs and highlight innovative technologies in this area, we discuss advantages of using commercially available handheld meters for translating IVDs from centralized labs to POC settings. We then provide comprehensive coverage of different signal transduction strategies to repurpose the commercially-available handheld meters, including personal glucose meter, pH meter, thermometer and pressure meter, for detecting a wide range of targets by integrating biochemical assays with the meters for POC testing. Finally, we identify remaining challenges and offer future outlook in this area.

Portable Aptasensor of Aflatoxin B1 in Bread Based on a Personal Glucose Meter and DNA Walking Machine

Despite some recent developments on the portable on-site sensor of Aflatoxin B1 (AFB1), the complex and expensive preparation of recognition elements have still limited their wide applications. In this paper, using the fast, low-cost, and stable recognition of aptamer DNA-AFB1, a portable aptasensor was constructed for the on-site detection of AFB1 in food matrixes, with the readout of personal glucose meter (PGM) and DNA walking machine for signal probe separation. In such an assay protocol, the target could trigger the DNA walker to autonomously move on the electrode surface, propelled by unidirectional Pb²⁺-specific DNAzyme digestion, which could amplify the signal and separate the signal probe as well for further quantification by the PGM. Under optimized conditions, the increase of PGM signal was relative with the concentration of AFB1 ranging from 0.02 to 10 nM and the low limit of detection (LOD) was 10 pM (S/N = 3). With the features of portability, and cheapness, the presented user-friendly method could be extended to various other analytes for wide point-of-care applications.

Highly specific and rapid glycan based amperometric detection of influenza viruses

Rapid and precise detection of influenza viruses in a point of care setting is critical for applying appropriate countermeasures. Current methods such as nucleic acid or antibody based techniques are expensive or suffer from low sensitivity, respectively. We have developed an assay that uses glucose test strips and a handheld potentiostat to detect the influenza virus with high specificity. Influenza surface glycoprotein neuraminidase (NA), but not bacterial NA, cleaved galactose bearing substrates, 4,7di-OMe N-acetylneuraminic acid attached to the 3 or 6 position of galactose, to release galactose. In contrast, viral and bacterial NA cleaved the natural substrate, N-acetylneuraminic acid attached to the 3 or 6 position of galactose. The released galactose was detected amperometrically using a handheld potentiostat and dehydrogenase bearing glucose test strips. The specificity for influenza was confirmed using influenza strains and different respiratory pathogens that include Streptococcus pneumoniae and Haemophilus influenzae; bacteria do not cleave these molecules. The assay was also used to detect co-infections caused by influenza and bacterial NA. Viral drug susceptibility and testing with human clinical samples was successful in 15 minutes, indicating that this assay could be used to rapidly detect influenza viruses at primary care or resource poor settings using ubiquitous glucose meters.

Double-Enzymes-Mediated Bioluminescent Sensor for Quantitative and Ultrasensitive Point-of-Care Testing

We report an ultrasensitive, quantitative, and rapid bioluminescent immunosensor (ABS) for point-of-care testing (POCT) of the disease biomarker in clinical samples using double enzymes including alkaline phosphatase (ALP) and luciferase. In the presence of the biomarker, the ALP attached on the surface of immuno-nanocomplex dephosphorylates adenine triphosphate (ATP), subsequently inhibiting the ATP-luciferin-luciferase bioluminescent reaction. The highly sensitive response of ATP (picomolar level) allows for ultrasensitive detection of biomarker via the effective change of the bioluminescence intensity through ALP- and luciferase-catalyzed reactions, which can be quantitatively determined by a portable ATP detector. This ABS fulfills the criteria for POCT that performs sensitive (femtomolar level of biomarkers) and quantitative measurement quickly (less than 1 h) with minimal equipment (portable detector).

Paper-based capacitive sensors for identification and quantification of chemicals at the point of care

The identification and quantification of chemicals play a vital role in evaluation and surveillance of environmental health and safety. However, current techniques usually depend on costly equipment, professional staff, and/or essential infrastructure, limiting their accessibility. In this work, we develop paper-based capacitive sensors (PCSs) that allow simple, rapid identification and quantification of various chemicals from microliter size samples with the aid of a handheld multimeter. PCSs are low-cost parallel-plate capacitors (~$0.01 per sensor) assembled from layers of aluminum foil and filter paper via double-sided tape. The developed PCSs can identify different kinds of fluids (e.g., organic chemicals) and quantify diverse concentrations of substances (e.g., heavy metal ions) based on differences in dielectric properties, including capacitance, frequency spectrum, and dielectric loss tangent. The PCS-based method enables chemical identification and quantification to take place much cheaply, simply, and quickly at the point-of-care (POC), holding great promise for environmental monitoring in resource-limited settings.

Transforming the blood glucose meter into a general healthcare meter for in vitro diagnostics in mobile health

Recent advances in mobile network and smartphones have provided an enormous opportunity for transforming in vitro diagnostics (IVD) from central labs to home or other points of care (POC). A major challenge to achieving the goal is a long time and high costs associated with developing POC IVD devices in mobile Health (mHealth). Instead of developing a new POC device for every new IVD target, we and others are taking advantage of decades of research, development, engineering and continuous improvement of the blood glucose meter (BGM), including those already integrated with smartphones, and transforming the BGM into a general healthcare meter for POC IVDs of a wide range of biomarkers, therapeutic drugs and other analytical targets. In this review, we summarize methods to transduce and amplify selective binding of targets by antibodies, DNA/RNA aptamers, DNAzyme/ribozymes and protein enzymes into signals such as glucose or NADH that can be measured by commercially available BGM, making it possible to adapt many clinical assays performed in central labs, such as immunoassays, aptamer/DNAzyme assays, molecular diagnostic assays, and enzymatic activity assays onto BGM platform for quantification of non-glucose targets for a wide variety of IVDs in mHealth.

Enzyme-Encapsulated Liposome-Linked Immunosorbent Assay Enabling Sensitive Personal Glucose Meter Readout for Portable Detection of Disease Biomarkers

There is considerable demand for sensitive, selective, and portable detection of disease-associated proteins, particularly in clinical practice and diagnostic applications. Portable devices are highly desired for detection of disease biomarkers in daily life due to the advantages of being simple, rapid, user-friendly, and low-cost. Herein we report an enzyme-encapsulated liposome-linked immunosorbent assay for sensitive detection of proteins using personal glucose meters (PGM) for portable quantitative readout. Liposomes encapsulating a large amount of amyloglucosidase or invertase are surface-coated with recognition elements such as aptamers or antibodies for target recognition. By translating molecular recognition signal into a large amount of glucose with the encapsulated enzyme, disease biomarkers such as thrombin or C-reactive protein (CRP) can be quantitatively detected by a PGM with a high detection limit of 1.8 or 0.30 nM, respectively. With the advantages of portability, ease of use, and low-cost, the method reported here has potential for portable and quantitative detection of various targets for different POC testing scenarios, such as rapid diagnosis in clinic offices, health monitoring at the bedside, and chemical/biochemical safety control in the field.

Adaptive use of a personal glucose meter (PGM) for acute biotoxicity assessment based on the glucose consumption of microbes

In this study, a new method for acute biotoxicity assessment was proposed by measuring the glucose consumption of microbes with a personal glucose meter (PGM).