Eliminating viscosity bias in lateral flow tests.

Despite the widespread application of point-of-care lateral flow tests, the viscosity dependence of these assay results remains a significant challenge. Here, we employ centrifugal microfluidic flow control through the nitrocellulose membrane of the strip to eliminate the viscosity bias. The key feature is the balancing of the sample flow into the cassette of the lateral flow test with the air flow out of the cassette. A viscosity-independent flow rate of 3.01 ± 0.18 µl/min (±6%) is demonstrated for samples with viscosities ranging from 1.1 mPas to 24 mPas, a factor greater than 20. In a model human IgG lateral flow assay, signal-intensity shifts caused by varying the sample viscosity from 1.1 mPas to 2.3 mPas could be reduced by more than 84%.

Rapid Detection of Pathogens in Wound Exudate via Nucleic Acid Lateral Flow Immunoassay.

The rapid detection of pathogens in infected wounds can significantly improve the clinical outcome. Wound exudate, which can be collected in a non-invasive way, offers an attractive sample material for the detection of pathogens at the point-of-care (POC). Here, we report the development of a nucleic acid lateral flow immunoassay for direct detection of isothermally amplified DNA combined with fast sample preparation. The streamlined protocol was evaluated using human wound exudate spiked with the opportunistic pathogen Pseudomonas aeruginosa that cause severe health issues upon wound colonization. A detection limit of 2.1 × 105 CFU per mL of wound fluid was achieved, and no cross-reaction with other pathogens was observed. Furthermore, we integrated an internal amplification control that excludes false negative results and, in combination with the flow control, ensures the validity of the test result. The paper-based approach with only three simple hands-on steps has a turn-around time of less than 30 min and covers the complete analytical process chain from sample to answer. This newly developed workflow for wound fluid diagnostics has tremendous potential for reliable pathogen POC testing and subsequent target-oriented therapy.

Flow control for lateral flow strips with centrifugal microfluidics.

Lateral flow strips (LFSs) are widely used for clinical diagnostics. The restricted flow control of the current designs is one challenge to the development of quantitative and highly sensitive LFSs. Here, we present a flow control for LFSs using centrifugal microfluidics. In contrast to previously presented implementations of lateral flow membranes into centrifugal microfluidic cartridges, we direct the flow radially outwards through the membrane. We control the flow using only the centrifugal force, thus it is independent of membrane wetting properties and permeability. The flow rate can be decreased and increased, enabling control of incubation times for a wide variety of samples. We deduced a formula as a guideline for the integration of chromatographic membranes into centrifugal microfluidic disks to ensure that all the sample liquid flows through the membrane, hence safely avoiding bypass flow around the membrane. We verified the calculated operation conditions using different membranes, different flow rates, and different sample viscosities.