Lateral flow test

Abstract: The lateral flow test has become the standard bioassay format in low-resource settings because it is rapid, easy to use, and low in cost, uses reagents stored in dry form, and is equipment-free. However, lateral flow tests are often limited to a single chemical delivery step and not capable of the multistep processing characteristic of high performance laboratory-based assays. To address this limitation, we are developing a paper network platform that extends the conventional lateral flow test to two dimensions; this allows incorporation of multistep chemical processing, while still retaining the advantages of conventional lateral flow tests. Here, we demonstrate this format for an easy-to-use, signal-amplified sandwich format immunoassay for the malaria protein PfHRP2. The card contains reagents stored in dry form such that the user need only add sample and water. The multiple flows in the device are activated in a single user step of folding the card closed; the configuration of the paper network automa...

Abstract: A new aptamer-based lateral flow strip assay has been designed and developed for on-site rapid detection of cortisol in sweat. Cortisol in sweat has been identified as a key biomarker to monitor physiological stress. A highly sensitive and specific cortisol sensor was achieved by conjugating cortisol-selective aptamers to the surface of gold nanoparticles (AuNPs). Aptamer-functionalized AuNPs are stable against salt-induced aggregation. When cortisol molecules are present in the sample, they interact with the designed aptamers causing their desorption from the AuNP surface. Free AuNPs can then be captured by reaction with cysteamine immobilized on the test zone of the lateral flow test strip. This enables the visual detection of cortisol within minutes. Important parameters that affect the detection sensitivity in both solution and lateral flow assays, such as the loading density of aptamers per AuNP, salt and cysteamine concentrations, were investigated to provide the optimum assay performance. This hand-held device successfully exhibited a visual limit of detection of 1 ng/mL, readily covering the normal range of free cortisol in sweat (8–140 ng/mL). No significant cross reactivity to other stress biomarkers was observed. The advantages of this paper-based biosensor over previously reported test strips include the use of aptamers (which are more stable, simpler to use and lower cost than antibodies) and a simplified lateral flow assay (LFA) strip design (without the use of complementary aptamers in the test line). The resulting LFA aptasensor provides a rapid, sensitive, user-friendly and cost-effective point of care device for cortisol detection in sweat and other biofluids.

Abstract: Sensitive and quantitative detection of protein biomarkers with a point-of-care (POC) assay is significant for early diagnosis, treatment, and prognosis of diseases. In this paper, a quantitative lateral flow assay with high sensitivity for protein biomarkers was established by utilizing fluorescent nanospheres (FNs) as reporters. Each fluorescent nanosphere (FN) contains 332 ± 8 CdSe/ZnS quantum dots (QDs), leading to its superstrong luminescence, 380-fold higher than that of one QD. Then a detection limit of 27.8 pM C-reaction protein (CRP) could be achieved with an immunofluorescent nanosphere (IFN)-based lateral flow test strip. The assay was 257-fold more sensitive than that with a conventional Au-based lateral flow test strip for CRP detection. Besides, the fluorescence intensity of FNs and bioactivity of IFNs were stable during 6 months of storage. Hence, the assay owns good reproducibility (intra-assay variability of 5.3% and interassay variability of 6.6%). Furthermore, other cancer biomarkers (PSA, CEA, AFP) showed negative results by this method, validating the excellent specificity of the method. Then the assay was successfully applied to quantitatively detect CRP in peripheral blood plasma samples from lung cancer and breast cancer patients, and healthy people, facilitating the diagnosis of lung cancer. It holds a good prospect of POC protein biomarker detection.

Abstract: Although the accessibility of HIV treatment in developing nations has increased dramatically over the past decade, viral load testing to monitor the response of patients receiving therapy is often unavailable. Existing viral load technologies are often too expensive or resource-intensive for poor settings, and there is no appropriate HIV viral load test currently available at the point-of-care in low resource settings. Here, we present a lateral flow assay that employs gold nanoparticle probes and gold enhancement solution to detect amplified HIV RNA quantitatively. Preliminary results show that, when coupled with nucleic acid sequence based amplification (NASBA), this assay can detect concentrations of HIV RNA that match the clinically relevant range of viral loads found in HIV patients. The lateral flow test is inexpensive, simple and rapid to perform, and requires few resources. Our results suggest that the lateral flow assay may be integrated with amplification and sample preparation technologies to serve as an HIV viral load test for low-resource settings.