Lateral Flow Immunoassays - from Paper Strip to Smartphone Technology

Superparamagnetic nanoarchitectures for disease-specific biomarker detection

Synthesis, bio-functionalization, and multifunctional activities of superparamagnetic-nanostructures have been extensively reviewed with a particular emphasis on their uses in a range of disease-specific biomarker detection and associated challenges.

Significant Sensitivity Improvement for Camera-Based Lateral Flow Immunoassay Readers

Recent developments in smartphone-based strip readers have further improved the performances of lateral flow test kits. Most smartphone cameras encode an unaltered and nonlinear power-law transfer function that maps the light intensity to a pixel value; this poses some limitations for camera-based strip readers. For faint-color test lines which are almost as white such as with nitrocellulose pads, the slope of the transfer function is low. Therefore, it is difficult to differentiate between the faint test lines and the white background. We show that by manually setting the camera exposure time-instead of using the automatic settings-to the high-slope region of the transfer function, the reader's sensitivity can be improved. We found that the sensitivity and the limit of detection of the Acidovorax avenae subsp. citrulli (Aac) test kit were enhanced up to 3-fold and 5-fold, respectively, when using the readers at the optimal camera settings, compared to the automatic mode settings. This simple technique can be readily applied to any existing camera-based colorimetric strip reader to significantly improve its performance.

Development of Immunochromatographic Assay for Determination of Tetracycline in Human Serum

Determining antibiotic concentration in human blood provides useful pharmacokinetic information. Commonly used methods such as ELISA require a long time to obtain results and thus cannot be applied when information is needed immediately. In this study, a novel antibody-based lateral flow technique was developed for tetracycline detection in human serum. Contrary to tests developed to analyze food samples, the features of work with serum as analyzed probe were studied for the first time here. The application of labeled and unlabeled specific antibodies was compared. For this purpose, specific and anti-species antibodies were labeled with gold nanoparticles and used for antigen⁻antibody interaction on the membrane surface with observed staining in the test zone. For both schemes, optimal conditions were established to provide the best sensitivity. The developed assay has a limit of visual detection as low as 35 and 11 ng/mL for the direct and indirect labeled antibodies, respectively. The limit of instrumental detection is from 0.4 to 3.5 ng/mL for diluted and undiluted sera. The use of indirect antibody labeling showed a small increase in sensitivity compared to traditional direct antibody labeling. The developed method showed no cross-reactivity with antibiotics of other classes. The method was used to test samples of serum. The results showed high correlation with the data obtained by ELISA (R² = 0.98968). The assay provides a quick assessment of the amount of antibiotics in the blood and keeps them under control throughout the duration of therapy.

Detection of Human Chorionic Gonadotropin (hCG) Hormone using Digital Lateral Flow Immunoassay

The main goal of this work was to establish a hybrid device incorporating an electrochemical-based transducer on a conventional lateral flow assay strip in order to perform an on-chip fast testing method for the detection of various bio-analyses. In this context, the expected development of the digital lateral-flow immunoassay to be considered a reliable low-cost instrument improves the future of the very simple and flexible approach oflateral-flow assays. It is anticipated to achieve a digital quantitative lateral-flow immunoassay by exploring the electrochemical transducers alongwith recognition elements for digitization of commercially available rapid tests. As a preliminary step, the described technique will be validated using two standard electrochemical measurements (amperometric and impedimetric) across two electrodes fixed onto the surface of LFA strip. The LFA strips were prepared at the factory for pregnancy tests and modified by adding two parallel copper electrodes at the lab. These strips were proven by in-vitro experiments to be reusable lasting for 20-30 multiple days. Further on, the detection of hCG Ab-Ag interaction using these strips was performed. Two different types of measurements, namely amperometric and impedimetric, were used which yielded similar results to those reported in literature with screen-printed micro-electrodes. In addition, different concentrations of NaCl and hCG Ag solution were investigated. However, the expected linear concentration response was obtained. A promising proof-of-concept have been achieved through this study. Further studies are needed to complete the development of fully printed disposable electrochemical devices that are able to either display a digital result directly or transmit data to a mobile phone using RFID/NFC.

PhoneQuant: A smartphone-based quantitative immunoassay analyser

There is a vital need for portable and cost-effective point-of-care (PoC) testing technologies that provide reliable and rapid results. Lateral Flow Immunoassays (LFIA) are suitable PoC diagnostic tools with the potential for use in a wide variety of field applications ranging from uses in clinical diagnostics to aiding law enforcement. Quick and reliable diagnosis of non-communicable diseases (NCD) like diabetes is vital especially in developing countries like India where the burden of these diseases is very high and is increasing day by day. In this paper, we have presented the design of smartphone-based fully quantitative LFIA analyser, An automatic image processing algorithm is also described. A repeatability study was done with stable fluorescence reference cartridges. The Coefficient of Variation (CoV) for repeatability study was calculated and it was found to be good (<; 1.5%). The instrument was tested with blood samples to generate a calibration curve for Glycated Haemoglobin (HbA1c) with respect to standard lab instrument. Three different set of settings parameters were used in smartphone camera their calibration curve formed. All three curves were linearly correlated with R²-value greater than 0.985. Finally, the calibration curve was validated through three HbA1c blood sample tests- for each sample, CoV was less than 5%. The PhoneQuant analyser is the portable cost-effective solution to traditional bulky LFIA analysers and it has good potential to be deployed at physician's desk or for in-home PoC testing for quick and reliable diagnosis.

Aptasensor based on fluorophore-quencher nano-pair and smartphone spectrum reader for on-site quantification of multi-pesticides

Current techniques for the detection of multi-pesticides are limited by technical complexity, sensitivity and cost. There is an urgent demand of developing new specific recognition elements and sensitive signal readouts for on-site monitoring. In this work, we developed a fluorescent aptamer-based lateral flow biosensor (apta-LFB) integrated with fluorophore-quencher nano-pairs and a smartphone spectrum reader to accomplish triple-target detection of chlorpyrifos, diazinon, and malathion. Aptamers serve as alternative recognition elements instead of antibodies in LFB, offering better specificity and stability. A novel fluorophore-quencher nano-pair (quantum dots nanobeads and gold nanostars) was implemented to perform "signal-on" instead of "signal-off". After optimization, detection limit of chlorpyrifos, diazinon, and malathion were determined to be 0.73 ng/mL, 6.7 ng/mL, and 0.74 ng/mL, respectively. Greatly increased sensitivity may come from the combination of improved signal and zero background. This innovative cascade strategy allowed to lower the detection limit of pesticides residue level in food, which is largely considered satisfactory. The accuracy and practicality of this design for effective on-site quantification of multi-pesticides were further confirmed using 12 vegetable and fruit samples. The estimated recoveries were between 82.4% and 112.8% in spiked vegetable samples, which indicated that the developed method is capable for detecting multi-pesticides in food samples. This sensitive handheld-system is promising to become a powerful tool for practical on-site application of multi-pesticide quantification procedures.

Mobile Phone Sensing of Cocaine in a Lateral Flow Assay Combined with a Biomimetic Material

Lateral flow assays (LFAs) are an ideal choice for drug abuse testing favored by their practicability, portability, and rapidity. LFA based on-site rapid screening devices provide positive/negative judgment in a short response time. The conventionally applied competitive assay format used for small molecule analysis such as abused drugs restricts the quantitation ability of LFA strips. We report herein, for the first time, a new strategy using the noncompetitive assay format via a biomimetic material, namely, poly(p-phenylene) β-cyclodextrin poly(ethylene glycol) (PPP-CD-g-PEG) combined with gold nanoparticle (AuNP) conjugates as the labeling agent to recognize the target cocaine molecule in the test zone. The intensities of the visualized red color in the test line indicate that the cocaine concentrations were analyzed via a smartphone application. Significantly, a combination of this platform with a smartphone application provides quantitative data on the cocaine amount, making it a very inventive and attractive approach especially for on-site applications at critical points such as traffic stops and the workplace.

Point-of-Care-Testing in Acute Stroke Management: An Unmet Need Ripe for Technological Harvest

Stroke, the second highest leading cause of death, is caused by an abrupt interruption of blood to the brain. Supply of blood needs to be promptly restored to salvage brain tissues from irreversible neuronal death. Existing assessment of stroke patients is based largely on detailed clinical evaluation that is complemented by neuroimaging methods. However, emerging data point to the potential use of blood-derived biomarkers in aiding clinical decision-making especially in the diagnosis of ischemic stroke, triaging patients for acute reperfusion therapies, and in informing stroke mechanisms and prognosis. The demand for newer techniques to deliver individualized information on-site for incorporation into a time-sensitive work-flow has become greater. In this review, we examine the roles of a portable and easy to use point-of-care-test (POCT) in shortening the time-to-treatment, classifying stroke subtypes and improving patient's outcome. We first examine the conventional stroke management workflow, then highlight situations where a bedside biomarker assessment might aid clinical decision-making. A novel stroke POCT approach is presented, which combines the use of quantitative and multiplex POCT platforms for the detection of specific stroke biomarkers, as well as data-mining tools to drive analytical processes. Further work is needed in the development of POCTs to fulfill an unmet need in acute stroke management.

Analytical Tools to Improve Optimization Procedures for Lateral Flow Assays

Immunochromatographic or lateral flow assays (LFAs) are inexpensive, easy to use, point-of-care medical diagnostic tests that are found in arenas ranging from a doctor’s office in Manhattan to a rural medical clinic in low resource settings. The simplicity in the LFA itself belies the complex task of optimization required to make the test sensitive, rapid and easy to use. Currently, the manufacturers develop LFAs by empirical optimization of material components (e.g., analytical membranes, conjugate pads and sample pads), biological reagents (e.g., antibodies, blocking reagents and buffers) and the design of delivery geometry. In this paper, we will review conventional optimization and then focus on the latter and outline analytical tools, such as dynamic light scattering and optical biosensors, as well as methods, such as microfluidic flow design and mechanistic models. We are applying these tools to find non-obvious optima of lateral flow assays for improved sensitivity, specificity and manufacturing robustness.

Point-of-care detection of extracellular vesicles: Sensitivity optimization and multiple-target detection

Extracellular vesicles (EVs) are membrane-bound nanovesicles delivered by different cellular lineages under physiological and pathological conditions. Although these vesicles have shown relevance as biomarkers for a number of diseases, their isolation and detection still has several technical drawbacks, mainly related with problems of sensitivity and time-consumed. Here, we reported a rapid and multiple-targeted lateral flow immunoassay (LFIA) system for the detection of EVs isolated from human plasma. A range of different labels (colloidal gold, carbon black and magnetic nanoparticles) was compared as detection probe in LFIA, being gold nanoparticles that showed better results. Using this platform, we demonstrated that improvements may be carried out by incorporating additional capture lines with different antibodies. The device exhibited a limit of detection (LOD) of 3.4×10⁶EVs/µL when anti-CD81 and anti-CD9 were selected as capture antibodies in a multiple-targeted format, and anti-CD63 labeled with gold nanoparticles was used as detection probe. This LFIA, coupled to EVs isolation kits, could become a rapid and useful tool for the point-of-care detection of EVs, with a total analysis time of two hours.