A lab-on-a-chip for detection of nerve agent sarin in blood

Abstract

Sarin (C(4)H(10)FO(2)P,O-isopropyl methylphosphonofluoridate) is a colourless, odourless and highly toxic phosphonate that acts as a cholinesterase inhibitor and disrupts neuromuscular transmission. Sarin and related phosphonates are chemical warfare agents, and there is a possibility of their application in a military or terrorist attack. This paper reports a lab-on-a-chip device for detecting a trace amount of sarin in a small volume of blood. The device should allow early detection of sarin exposure during medical triage to differentiate between those requiring medical treatment from mass psychogenic illness cases. The device is based on continuous-flow microfluidics with sequential stages for lysis of whole blood, regeneration of free nerve agent from its complex with blood cholinesterase, protein precipitation, filtration, enzyme-assisted reaction and optical detection. Whole blood was first mixed with a nerve gas regeneration agent, followed by a protein precipitation step. Subsequently, the lysed product was filtered on the chip in two steps to remove particulates and fluoride ions. The filtered blood sample was then tested for trace levels of regenerated sarin using immobilised cholinesterase on the chip. Activity of immobilised cholinesterase was monitored by the enzyme-assisted reaction of a substrate and reaction of the end-product with a chromophore. Resultant changes in chromophore-induced absorbance were recorded on the chip using a Z-shaped optical window. Loss of enzyme activity obtained prior and after passage of the treated blood sample, as shown by a decrease in recorded absorbance values, indicates the presence of either free or regenerated sarin in the blood sample. The device was fabricated in PMMA (polymethylmethacrylate) using CO(2)-laser micromachining. This paper reports the testing results of the different stages, as well as the whole device with all stages in the required assay sequence. The results demonstrate the potential use of a field-deployable hand-held device for point-of-care triage of suspected nerve agent casualties.

Bonding of thermoplastic polymer microfluidics

“…This feature, together with the relatively high bond strengths and overall simplicity of the approach, have made direct thermal bonding the most common method for sealing microfluidic chips. Thermal fusion bonding of various thermoplastics has been widely demonstrated, including PC Wang et al 2005;Park et al 2008;Shadpour et al 2007;Wang et al 2008), PMMA (Chen et al 2003;Arroyo et al 2007;Kelly and Woolley 2003;Liu et al 2008;Nie and Fung 2008;Nikcevic et al 2007;Sun et al 2006;Tan et al 2008;Yao et al 2005;Zhu et al 2007), and COC Bhattacharyya and Klapperich 2006;Riegger et al 2007;Tsao et al 2008;Steigert et al 2007;Fredrickson et al 2006;Olivero and Fan 2008). Direct thermal bonding of a wide range of polymers including polystyrene, nylon, polysulfone ) as well as polystyrene and copolyester ) have also been explored.…”

“…Several general methodologies have been explored to reduce the degree of channel collapse during thermal bonding. The first approach relies on the use of high bond temperatures as high as 58°C above the substrate T g , while applying low pressures to limit substrate deformation (Sun et al 2006;Tan et al 2008). Using this approach, excellent stability of channel cross-sections can be attained, as revealed in Fig.…”

Enzymeless determination of total sugar by luminol–tetrachloroaurate chemiluminescence on chip to analyze food samples

“…The CL intensity emitted from the equivalent concentration of reactants increased as the flow rate increased. Solution mixing in a microchannel is improved when the flow rate is high due to chaotic advection [24]. In this case, vigorous mixing occurred at a higher flow rate due to the generation of faster vortexes, which led to increasing contact with the reactant and thus brighter CL emission.…”

Microfluidic Chips for Point‐of‐Care Immunodiagnostics

“…[ 65 ] Microfl uidic fl ow paths are printed onto thermally shrinkable polystyrene sheets [ 66 ] and laser ablation is used to micromachine PMMA chips. [ 67 ] Arbitrary microchannels can be formed on demand by micropatterned light irradiation or injection molding for mass fabrication to produce disposable one-use devices. [ 36 ] There are a wide variety of polymers available, which have various optical properties, glass transition temperatures, chemical resistance and permeability to gases and liquids.…”