Paper-based Lateral Flow Assay Research Articles

Lateral flow aptamer assay for detection of aflatoxin B1 in tea using upconversion nanoparticles

Aflatoxin, extensively existing in peanuts, corn, rice, soybeans, wheat and tea, is a type of mycotoxins with the highest toxicity and carcinogenicity and thus poses a serious threat to human health. In this article, upconversion nanoparticles modified with aptamers specific to aflatoxin B1 were used as fluorescence markers. By this way, we constructed a paper-based lateral flow assays detection technology for rapid detection of aflatoxin B1 with good linearity in the concentration range of 0.1–100 ng/mL and detection limit of 0.03 ng/mL. This method can realize quantitative detection of aflatoxin B1 in real tea sample with high sensitivity and specificity. Hence it is suitable for rapid on - site detection of aflatoxin B1 by utilizing this method, which shows good economic value and application prospects.

Highly sensitive paper-based immunoassay using photothermal laser speckle imaging

Paper-based lateral-flow assay (LFA) is a simple and inexpensive point-of-care device that has become commonplace in medicine, environmental monitoring, and over-the-counter personal use. Some LFAs have demonstrated comparable analytical performance with laboratory-based methods, but the detection limit or sensitivity of most LFAs is significantly inferior to other molecular techniques by 10–100 × . Consequently, LFAs are not viable for the early detection of disease-relevant biomarkers that are present in extremely small amounts in clinical specimens. Herein, we present a simple, cost-effective, and highly sensitive LFA sensor based on photothermal laser speckle imaging (PT-LSI). Under the illumination of a photothermal excitation light, gold nanoparticles (AuNPs), a common signal transduction medium in LFAs, absorb the light energy to produce heat, which subsequently induces modulation of the optical property and thermal deformation of the membrane. We measured these fluctuations through laser speckle imaging to quantify the concentration of AuNP-biomarker complexes. We experimentally demonstrate that the detection limit of our technique is superior to that of colorimetric detector by 68–125 × . The capability of our sensor for highly sensitive detection of disease biomarkers is validated by using U.S. FDA-approved LFA kits for cryptococcal antigens (CrAg).

Correcting the effect of hematocrit in whole blood coagulation analysis on paper-based lateral flow device

A simple method to correct the effect of hematocrit (Hct) on a paper-based lateral flow assay device that is designed to assess whole blood coagulation is reported.

Determination of glycated albumin using boronic acid-derived agarose beads on paper-based devices

Self-monitoring of glycated albumin (GA), a useful glycemic marker, is an established method for preventing diabetes complications. Here, the paper-based lateral flow assay devices were developed for the sensitive detection of GA and the total human serum albumin (tHSA) in self-monitoring diabetes patients. Boronic acid-derived agarose beads were packed into a hole on a lateral flow channel. These well-coordinated agarose beads were used to capture GA through specific cis-diol interactions and to enhance the colorimetric signals by concentrating the target molecules. The devices exhibited large dynamic ranges (from 10 μg/ml to 10 mg/ml for GA and from 10 mg/ml to 50 mg/ml for tHSA) and low detection limits (7.1 μg/ml for GA and 4.7 mg/ml for tHSA), which cover the range of GA concentration in healthy plasma, which is 0.21-1.65 mg/ml (0.6%-3%). In determining the unknown GA concentrations in two commercial human plasma samples, the relative percentage difference between the values found by a standard ELISA kit and those found by our developed devices was 2.62% and 8.80%, which are within an acceptable range. The measurements of GA and tHSA were completed within 20 min for the total sample-to-answer diagnosis, fulfilling the demand for rapid analysis. Furthermore, the recovery values ranged from 99.4% to 110% in device accuracy tests. These results indicate that the developed paper-based device with boronic acid-derived agarose beads is a promising platform for GA and tHSA detection as applied to self-monitoring systems.

Novel functionalities of hybrid paper-polymer centrifugal devices for assay performance enhancement.

The presented work demonstrates novel functionalities of hybrid paper-polymer centrifugal devices for assay performance enhancement that leverage the advantages of both paper-based and centrifugal microfluidic platforms. The fluid flow is manipulated by balancing the capillary force of paper inserts with the centrifugal force generated by disc rotation to enhance the signal of a colorimetric lateral flow immunoassay for pathogenic E. coli. Low-cost centrifugation for pre-concentration of bacteria was demonstrated by sample sedimentation at high rotational speeds before supernatant removal by a paper insert via capillary force after deceleration. The live bacteria capture efficiency of the device was similar to a commercial centrifuge. This pre-concentrated sample when combined with gold nanoparticle immunoconjugate probes resulted in a detection limit that is 10× lower than a non-concentrated sample for a lateral flow immunoassay. Signal enhancement was also demonstrated through rotational speed variation to prevent the flow for on-device incubation and to reduce the flow rate, thus increasing the sample residence time for the improved capture of gold nanoparticle-bacteria complexes in an integrated paper microfluidic assay. Finally, multiple sequential steps including sample pre-concentration, filtration, incubation, target capture by an integrated paper microfluidic assay, silver enhancement and quenching, and index matching were completed within a single device. The detection limit was 105 colony forming units per ml, a 100× improvement over a similar paper-based lateral flow assay. The techniques utilize the advantages of paper-based microfluidic devices, while facilitating additional functionalities with a centrifugal microfluidic platform for detection performance enhancement in a low-cost, automated platform amenable to point-of-care environments.

Relationship analysis of speech communication between salivary cortisol levels and personal characteristics using the Smartphone Linked Stress Measurement (SLSM)

Salivary cortisol is frequently used as a biomarker of stress. However, no study has used salivary cortisol to evaluate stress levels related to personal characteristics with a paper-based lateral flow assay (LFA) strip and a smartphone holder, and a smartphone at the same time during simulated speech communication. In this paper, we investigated variations in levels of salivary cortisol, communication apprehension, and the effects of self-efficacy via the Smartphone Linked Stress Measurement (SLSM) that we have recently reported. Saliva samples were collected by 48 participants (30 male and 18 female) at three moments: immediately before public speaking (basal measurement), immediately after public speaking (speech measurement), and forty minutes after taking a rest (relaxed measurement). Results from the questionnaire showed that salivary cortisol levels, communication apprehension, and self-efficacy were significantly correlated. Also, anxiety about speaking can raise their stress levels during their speeches, as reflected in their increased cortisol levels. Therefore, this study establishes the effects of self-efficacy on communication apprehension and salivary cortisol.

Developing new materials for paper-based diagnostics using electrospun nanofibers

The use of electrospun nanofibers as functional material in paper-based lateral flow assays (LFAs) was studied. Specific chemical features of the nanofibers were achieved by doping the base polymer, poly(lactic acid) (PLA), with poly(ethylene glycol) (PEG) and polystyrene8K-block-poly(ethylene-ran-butylene)25K-block-polyisoprene10K-Brij76 (K3-Brij76) (KB). The LFAs were assembled such that the sample flowed through the nanofiber mat via capillary action. Initial investigations focused on the sustainable spinning and assembly of different polymer structures to allow the LFA format. Here, it was found that the base polymer poly(vinyl alcohol) (PVA), which was shown to function well in microfluidic biosensors, did not work in the LFA format. In contrast, PLA-based nanofibers enabled easy assembly. Three relevant features were chosen to study nanofiber-based functionalities in the LFA format: adsorption of antibodies, quantification of results, and nonspecific binding. In particular, streptavidin-conjugated sulforhodamine B (SRB)-encapsulating liposomes were captured by anti-streptavidin antibodies adsorbed on the nanofibers. Varying the functional polymer concentration within the PLA base enabled the creation of distinct capture zones. Also, a sandwich assay for the detection of Escherichia coli O157:H7 was developed using anti-E. coli antibodies as capture and reporter species with horseradish peroxidase for signal generation. A dose-response curve for E. coli with a detection limit of 1.9 × 10(4) cells was achieved. Finally, functional polymers were used to demonstrate that nonspecific binding could be eliminated using antifouling block copolymers. The enhancement of paper-based devices using functionalized nanofibers provides the opportunity to develop a broad spectrum of sensitive and specific bioassays with significant advantages over their traditional counterparts.