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Type-I pyrethroids are frequently used for disinfection purposes on airplanes from and to tropical areas. The WHO (Word Health Organization) defines “disinfection” as the procedure whereby health measures are taken to control or kill the insect vectors of human diseases including dengue, yellow fever and malaria.1 Due to this, a new effective and rapid method for pyrethroids analysis directly in the plane is needed.
To detect type-I pyrethroids, gated materials are constructed for the purpose of finely tuning the movement of a cargo from voids of a mesoporous inorganic support to a solution, in response to a predefined stimulus.2 Antibodies are bound to specific functional groups grafted on the support’s surface with the two-fold aim of closing the mesopores and working as biological receptors for the target compounds.2 A specific opening mechanism, activated selectively in presence of pyrethroids as analytes, is able to control the release of an indicator dye previously loaded inside the inorganic support. As only few molecules of pyrethroids are necessary to open a pore and release a large amount of dyes, the system shows an intrinsic signal amplification quantified as a fluorescence emission intensity.3
Different mesoporous silica supports (from nano- and microparticles to platelets and short fibers) were synthetized, characterized and functionalized following different capping strategies. In this contribution, we will compare the temporal response behaviour of the optimized gated materials to verify if the respective delivery systems are properly closed and how fast they can be opened in presence of the analytes. Our results indicate that the trends of the kinetics observed in solution show a better control of the closing/opening mechanism when the epitope region of the antibody (around 10 nm) properly fits the pore size of the carriers.
Because the incorporation of an antibody-gated dye-delivery system with a conventional test-strip-based lateral-flow assay allows for the detection of analytes down to the ppb level in an easy-to-operate manner and an overall assay time of 2–5 min, which is fast for a biochemical test,3 we carried out first model studies for a lateral flow test assay on membranes, using a smartphone setup for read-out.
Rapid testing methods for the use directly at a point-of-need are expected to unfold their true potential especially when offering adequate capabilities for the simultaneous measurement of multiple analytes of interest. However, the implementation of multiplexing features while retaining simplicity, performance and portability is one of the prominent challenges in the field. Keeping in mind these challenges, we decided to combine the use of stimuli-responsive materials for small-molecule sensing relying on chemical signal amplification and their incorporation on paper strips for lateral-flow assays in a straightforward manner. Considering the modularity, high sensitivity and selectivity of antibody-gated indicator delivery systems, a multiplexed assay for three small-molecule explosives TATP, TNT and PETN was developed, allowing to detect the analytes simultaneously with a single test strip at lower ppb concentrations in liquid phase in <5 min, using a fluorescence reader or a smartphone for readout.
Because of the versatility of the hybrid material and the modularity of the assay architecture, it is obvious that this generic approach should be easily transferable to food or environmental analysis, point-of-care diagnostics and other areas of application in which the rapid screening for multiple parameters from liquid samples without clean-up in a dedicated laboratory is in demand.