Microneedle-based lateral flow immunoassays for rapid diagnostic testing

Lateral flow immunoassays (LFIAs) are one of the most commonly used tests to detect and screen for infectious diseases in the world. While these tests are simple, inexpensive and readily available, they suffer from several limitations. First, many LFIAs require a blood sample which involves trained medical personnel, poses risks of infection, and can complicate cooperation in young children and communities with blood taboos. Second, conventional LFIAs are comprised of multiple components and materials, which complicates the fabrication process and increases overall device costs. Third, LFIAs generally only provide qualitative results (i.e. positive vs. negative), which limits their diagnostic utility. To address these limitations, this research aims to investigate new approaches for developing LFIA platforms which do not require blood sampling, are simple to fabricate, and are capable of quantitative analytical measurements. We first explored the development of a microneedle-based LFIA patch for rapid protein detection in dermal interstitial fluid. This device integrates a hollow microneedle array for minimally invasive sample extraction with a colloid gold-based LFIA. A simple gold enhancement treatment was employed to enhance the detection sensitivity of this assay, and the underlying mechanism of this enhancement mechanism was elucidated through experimental investigation. For proof of concept, this device was used to detect Plasmodium falciparum histidine-rich protein 2 (PfHRP2), an important biomarker for malaria infection, in simulated interstitial fluid, which could be detected at concentrations down to 8 ng/mL. Furthermore, each test can be completed in less than 20 minutes and requires no equipment. We also developed a unique strategy for fabricating LFIAs on a single piece of cellulose paper via laser cutting. All of the components of a conventional LFIA, such as the sample, conjugate and absorbent pads and nitrocellulose membrane, are integrated on a single-layer cellulose paper "card". Various device parameters, such as the test strip geometry, composition of the blocking solution and amount of colloid gold-antibody conjugates, were optimized to minimize nonspecific binding of conjugates for enhanced detection sensitivity. The functionality of this assay was validated by using it to detect PfHRP2 in human plasma samples which could be detected at concentrations down to 4 ng/mL with excellent specificity.Lastly, towards a LFIA platform capable of quantitative analytical measurements, we have integrated an electrical impedance sensor with our single layer LFIA system. This device employs interdigitated sensing electrodes and an inductive coil antenna for wireless sensing using an impedance analyzer. A unique detection scheme is employed where the electrical properties of the sensing electrodes are monitored in response to surface immobilization of gold colloid-antibody conjugates. Device testing was carried out by performing quantitative measurements of PfHRP2 in buffer samples, which could be detected at concentrations down to 8 ng/mL. In conclusion, we have presented several unique LFIA platforms that offer simplified fabrication, ease of use and improved analytical performance compared with conventional LFIAs, which can ultimately enhance the usefulness of LFIA technology for point-of-care diagnostic testing.