Abstract
Measurement of the height of a packed column of cells or beads, which can be direclty related to the number of cells or beads present in a chamber, is an important step in a number of diagnostic assays. For example, haematocrit measurements may rapidly identify anemia or polycthemia. Recently, user-friendly and cost-efficient Lab-on-a-Chip devices have been developed towards isolating and counting cell sub-populations for diagnostic purposes. In this work, we present a low-cost optical module for estimating the filling level of packed magnetic beads within a Lab-on-a-Chip device. The module is compatible with a previously introduced, disposable microfluidic chip for rapid determination of CD4+ cell counts. The device is a simple optical microscope module is manufactured by 3D printing. An objective lens directly interrogates the height of packed beads which are efficiently isolated on the finger-actuated chip. Optionally, an inexpensive, battery-powered Light Emitting Diode may project a shadow of the microfluidic chip at approximately 50-fold magnification onto a nearby surface. The reader is calibrated with the filling levels of known concentrations of paramagnetic beads within the finger actuated chip. Results in direct and projector mode are compared to measurements from a conventional, inverted white-light microscope. All three read-out methods indicate a maximum variation of 6.5% between methods.
Highlights
Enumeration of cells, and of specific cell sub-populations, constitutes an important step in diagnostic assays and in life science research
In this paper we present an optical reader which is compatible with the chip introduced by Glynn et al [29] (Fig 1)
The microfluidic chips are prototyped using the method previously described by Glynn et al [29]
Summary
Enumeration of cells, and of specific cell sub-populations, constitutes an important step in diagnostic assays and in life science research. Cell-counting technologies, based on flow cytometry, are well established and have been widely used in research and clinical laboratories for decades [1]. These cytometers remain expensive and complex instruments suitable only for use in well-supported centralised laboratory environments. In order to make cell-enumeration based assays available at the ‘point-of-use’, in particular in low-resource settings, rugged, robust and low-cost systems for integrated cell-sorting and analysis are needed. While lacking the general flexibility of conventional flow cytometers, a range.
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