Lab-on-valve: universal microflow analyzer based on sequential and bead injection

Abstract

This paper introduces a novel methodology for downscaling reagent based assays to micro-and submicroliter level. It is shown that sample handling in the sequential injection mode, which employs forward, reversed and stopped flow, can be programmed to accommodate a wide variety of assays within the same microfluidic device. Solution metering, mixing, dilution, incubation and monitoring can be executed in any desired sequence in a system of channels, integrated with a multipurpose flow cell. The channel system and flow cell are fabricated as a monolithic structure mounted atop a conventional multiposition valve. In addition to compactness, the advantage of this 'lab-on-valve' system is the permanent rigid position of the sample processing channels that ensures repeatability of microfluidic manipulations, controlled by conventional sized peripherals. With the exception of the integrated microconduit system, that has been designed and mesofabricated by computer aided design (CAD) technology, all peripherals (sequential injection system, fiber optic UV/VIS spectrophotometer-fluorometer) are conventional sized and commercially available components. This provides proven robustness and reliability of operation, and makes the microfluidic system compatible with real life samples and peripheral instruments. The system has been characterized by dye injection, to provide guidelines for method development. Its versatility is documented by a phosphate assay, enzymatic activity assay of protease and by a bioligand interaction assay of immunoglobulin G (IgG) based on its interaction with protein G immobilized on Sepharose beads.

Determination of trace zinc in seawater by coupling solid phase extraction and fluorescence detection in the Lab-On-Valve format

“…Micro Sequential Injection Lab-On-Valve (µSI-LOV) manifolds alleviate the majority of the drawbacks of FIA methods [12][13][14][15]. This technique is thus an attractive approach for shipboard analysis of trace metals since LOV manifolds are compact, fully automated, and provide highly precise fluidic manipulations in a miniaturized flow manifold with minimal reagent consumption and waste production.…”

Miniaturization of environmental chemical assays in flowing systems: The lab-on-a-valve approach vis-à-vis lab-on-a-chip microfluidic devices

“…In fact, the LOV unit is devised to incorporate detection facilities, that is, optical devices (namely, diode-array spectrophotometers, charged-coupled devices (CCDs), laser-induced spectrofluorimeters or luminometers) where the communication to the detector and/or the light source are made via optical fibres (see Fig. 3), and where the position of the fibres can be used to adjust the optical light path of the cell [8]. The microfabricated channel system is also amenable to admit conventional sized peripheral devices, thus facilitating the hyphenation with a plethora of modern detection techniques/analytical instruments, such as electrothermal atomic absorption spectrometry [ 23 37 ], depending on the particular chemical assay.…”

“…Following sample loading and clean-up protocols, appropriate eluents can be aspirated, and the eluate propelled to either the flow-through cell or an external detection device, as sandwiched by air or immiscible liquid segments in order to preserve its integrity. The multipurpose flow cell can even be configured to admit bead particles, thereby serving as a platform for real-time monitoring of chemical events at solid surfaces [8], the exploration of cellular activities via immobilized living cells [ 38 , 39 ] as well as the investigation of biomolecular association and dissociation processes [26], as exploited in enzyme-linked immunosorbent assays [ 40 ] and affinity chromatographic methods [ 41 ]. Since the entire protocol sequence is computer controlled, all fluidic unit operations are readily to be re-programmed according to the involved chemistry.…”

“…The LOV microfluidic unit, however, offers a universal means for sample introduction as a result of its singular hardware configuration [8]. The central processing unit in the LOV monolithic structure has been designed to house a flow-through port (see port 5 in Figures 2 and 3), where one channel serves as the sample solution inlet while the other channel works as the sample outlet, which is plugged to an ancillary peristaltic pump.…”

“…And in 2000 it was extended by the third generation named the Lab-on-a-Valve (LOV) [ 8 ], which was initially spawned as a fluidic universal system for downscaling reagent-based assays to the micro-and submicroliter level. Yet it has concurrently proven to offer vast potentials for accommodation of a wide variety of sample processing steps in a micro-scale according to the requirements of the assays.…”