Flexible planar microfluidic chip employing a light emitting diode and a PIN-photodiode for portable flow cytometers

In situ fabricated 3D micro-lenses for photonic integrated circuits

Aspheric astigmatic polymer micro-lenses were fabricated directly onto photonic integrated circuits using two-photon lithography. We observed a 12.6 dB improvement in the free space coupling efficiency between integrated ridge laser pairs with micro-lenses to those without.

Photonic integration platform with pump free microfluidics

Chip based particle sensing using 3D capillary fill microfluidics integrated with monolithically integrated lasers and photodetectors is used to demonstrate the feasibility of true chip scale photonic measurements of fluids. The approach is scalable and manufactured using industry standard compound semiconductor fabrication tools. The need for fluid speed regulation via external pumps is removed by measuring local particle velocity at the point of interrogation and particle position within the fluid flow is derived from multiple time resolved forward scattered light signals. Particle size discrimination of 10 and 15 μm polystyrene microbeads is used as an example.

Self-contained microfluidic systems: a review

Microfluidic systems enable rapid diagnosis, screening and monitoring of diseases and health conditions using small amounts of biological samples and reagents. Despite these remarkable features, conventional microfluidic systems rely on bulky expensive external equipment, which hinders their utility as powerful analysis tools outside of research laboratories. 'Self-contained' microfluidic systems, which contain all necessary components to facilitate a complete assay, have been developed to address this limitation. In this review, we provide an in-depth overview of self-contained microfluidic systems. We categorise these systems based on their operating mechanisms into three major groups: passive, hand-powered and active. Several examples are provided to discuss the structure, capabilities and shortcomings of each group. In particular, we discuss the self-contained microfluidic systems enabled by active mechanisms, due to their unique capability for running multi-step and highly controllable diagnostic assays. Integration of self-contained microfluidic systems with the image acquisition and processing capabilities of smartphones, especially those equipped with accessory optical components, enables highly sensitive and quantitative assays, which are discussed. Finally, the future trends and possible solutions to expand the versatility of self-contained, stand-alone microfluidic platforms are outlined.

Optofluidic Device Based Microflow Cytometers for Particle/Cell Detection: A Review

Optofluidic devices combining micro-optical and microfluidic components bring a host of new advantages to conventional microfluidic devices. Aspects, such as optical beam shaping, can be integrated on-chip and provide high-sensitivity and built-in optical alignment. Optofluidic microflow cytometers have been demonstrated in applications, such as point-of-care diagnostics, cellular immunophenotyping, rare cell analysis, genomics and analytical chemistry. Flow control, light guiding and collecting, data collection and data analysis are the four main techniques attributed to the performance of the optofluidic microflow cytometer. Each of the four areas is discussed in detail to show the basic principles and recent developments. 3D microfabrication techniques are discussed in their use to make these novel microfluidic devices, and the integration of the whole system takes advantage of the miniaturization of each sub-system. The combination of these different techniques is a spur to the development of microflow cytometers, and results show the performance of many types of microflow cytometers developed recently.

Lab-on-chip cytometry based on magnetoresistive sensors for bacteria detection in milk

Flow cytometers have been optimized for use in portable platforms, where cell separation, identification and counting can be achieved in a compact and modular format. This feature can be combined with magnetic detection, where magnetoresistive sensors can be integrated within microfluidic channels to detect magnetically labelled cells. This work describes a platform for in-flow detection of magnetically labelled cells with a magneto-resistive based cell cytometer. In particular, we present an example for the validation of the platform as a magnetic counter that identifies and quantifies Streptococcus agalactiae in milk.

Sensitivity improvement in fluorescence-based particle detection

Microfluidic flow cytometers are highly interesting candidates for biomedical point-of-care applications. However, the sensitivity, reliability, and throughput of these systems must be improved to provide the full functionality of established flow cytometric systems. One proposed method to improve fluorescence detection systems is to use spatial modulation techniques. We derive the noise-related statistics and calculate the coefficient of variation for a detection system with and without spatial modulation. We measure the noise properties of a nonmodulated microfluidic fluorescence particle detection system and analyze the possible performance gains using spatial modulation.

Hybrid lithography: combining UV-exposure and two photon direct laser writing

We demonstrate a method for the combination of UV-lithography and direct laser writing using two-photon polymerization (2PP-DLW). First a dye doped photoresist is used for UV-lithography. Adding an undoped photoresist on top of the developed structures enables three-dimensional alignment of the 2PP-DLW structures by detecting the spatially varying fluorescence of the two photoresists. Using this approach we show three dimensional alignment by adding 3D structures made by 2PP-DLW to a previously UV-exposed structure. Furthermore, a fluidic system with an integrated total internal reflection mirror to observe particles in a microfluidic channel is demonstrated.