Lab on a stick: multi-analyte cellular assays in a microfluidic dipstick

Abstract

A new microfluidic concept for multi-analyte testing in a dipstick format is presented, termed "Lab-on-a-Stick", that combines the simplicity of dipstick tests with the high performance of microfluidic devices. Lab-on-a-stick tests are ideally suited to analysis of particulate samples such as mammalian or bacterial cells, and capable of performing multiple different parallel microfluidic assays when dipped into a single sample with results recorded optically. The utility of this new diagnostics format was demonstrated by performing three types of multiplex cellular assays that are challenging to perform in conventional dipsticks: 1) instantaneous ABO blood typing; 2) microbial identification; and 3) antibiotic minimum inhibitory (MIC) concentration measurement. A pressure balance model closely predicted the superficial flow velocities in individual capillaries, that were overestimated by up to one order of magnitude by the Lucas-Washburn equation conventionally used for wicking in cylindrical pores. Lab-on-a-stick provides a cost-effective, simple, portable and flexible multiplex platform for a range of assays, and will deliver a new generation of advanced yet affordable point-of-care tests for global diagnostics.

High Dynamic Range Bacterial Cell Detection in a Novel “Lab-In-A-Comb” for High-Throughput Antibiotic Susceptibility Testing of Clinical Urine Samples

“…Each comb consisted of a simple plastic paper binder (Office Depot, Andover UK) containing a row of Lab-on-a-Stick test strips made by a method adapted from a previous report demonstrating dipstick microfluidic minimum inhibitory concentration assays (21). The fluorinated ethylene propylene MCF was manufactured by melt-extrusion by Lamina Dielectrics Ltd (Billingshurst, West Sussex, UK) from a highly transparent fluorinated ethylene propylene co-polymer (FEP-Teflon®).…”

“…After 5 minutes of incubation, the excess solution was removed by manually injecting air using a 50 mL plastic syringe. All antibiotics were loaded at concentrations that would lead to release of the breakpoint concentration into the sample, taken from published data for E. coli (6), based on previously determined loading efficiency quantified by LC-MS (21).…”

“…We therefore exploited devices developed previously by our group which combine features of microfluidic devices and dipstick tests (such as uranalysis strips). We recently showed these "Lab-on-a-stick" devices were capable of performing classical functional microbiology tests (21). These devices used a hydrophilic polymer coating to internally modify a fluoropolymer microcapillary film (MCF) that contains a parallel array of ten ~200 micron diameter microcapillaries.…”

Design and Fabrication of Capillary-Driven Flow Device for Point-Of-Care Diagnostics

“…Glass/hydrophilic capillaries have also been used to drive flow via capillary action, as described by Lapierre et al [17], who used bare glass capillaries to collect blood samples. In contrast, fluoropolymer microcapillaries (FEP) have been coated with reagents to render their surface hydrophilic and draw up blood or aqueous samples in a minute fraction of time [18][19][20][21][22]. Pivetal et al [19] coated FEP capillaries with polyvinyl alcohol (PVA) to convert their surface from hydrophobic to hydrophilic and attached reagents or antibodies on the surface for the detection of protein biomarkers.…”

“…The FEP microcapillaries were multiplexed in parallel by injecting solutions into 10 capillaries at the same time, i.e., a PSA standard solution, detection antibodies, the enzyme complex, washing solutions and the enzymatic substrates, which were injected in the capillaries simultaneously. The FEP microcapillaries were placed vertically in a blood sample to draw up liquid for ABO blood typing [18]. As the liquid rose into the capillaries, the reagents were released into the sample and reacted with biomarkers to produce a colour or a fluorescent signal, which was then detected by microscope or portable/smartphone systems.…”