A multi-channel Excitation Optic for cost efficient Lab-on-chip Devices

While the gold standard for infection diagnostics remains the PCR test, the pandemic has shown the importance of Point-of-Care devices that carry the test in the field and yield results in an hour or less. Lab-on-Chip systems have been a game changer in this respect, but PCR based devices are still rather expensive. Among the main cost drivers are the optical readout modules that excite and detect fluorescence signals in multiple spectral channels. Depending on the device concept, the bulk of this cost is either shifted towards component cost, precise alignment, or complex mechanics, but there is a lack of compact, simple irradiation and detection modules that scale well in mass production. In this contribution we focus on the excitation optics, which must provide visible radiation in well-defined spectral bands that illuminate the sample. While the state of the art teaches either a precise assembly of dichroic mirrors or a filter changing mechanism, we have devised and demonstrated a concept that involves a holographic optical element (HOE). This HOE does not only act as a beam combiner, directing light from the individual sources towards the sample, but also exploits the intrinsic spectral selectivity for bandpass filtering, rendering any dielectric multilayer components obsolete. We present a 4-channel excitation optics with a single HOE at its core that unites light from four different LEDs towards a sample, demonstrating quantitative fluorescence readouts from fluorophore concentrations in the sub-micromolar range.