No abstract

A combination of fluorescence detection and microfluidic technology provides promising applications in life sciences. A prototype of an integrated fluorescence detection system and optical fiber light guide on a laminate-based multichannel microfluidic chip has been developed and tested. A blue LED, plastic optical fiber, photodiode, Mylar and PMMA, and fluorescein and BSA-FITC were used as an excitation source, light coupler and guide, detector, microfluidic substrate and sample, respectively. The results show that the system is capable of detecting weak fluorescence emission from a fluorescein solution at concentration down to 0.01 ng/ml, and gives linear response. The results were also reproducible, and no cross-talk between adjacent channels was observed. The test using BSA as a model analyte demonstrates its feasibility for on-chip immunosensor applications. The performance and applications can be developed further. This prototype can be used as a platform to develop a simple and compact bio-fluorescence detection system integrated with an inexpensive and disposable multichannel microfluidic chip for biomedical devices.

Development of a compact fluorescence-based detection system for use in a micro-analytical system, such as a point-of-care diagnostic system, often requires a multi-channel microfluidic chip system. Since the materials used for microfluidic chips usually are transparent in the visible region and have a refractive indices higher than that of air or the surrounding environment, the fluorescence emission and scattered excitation light can propagate through the chip. We observed that such propagation can cause cross-talk between adjacent channels, and may become the major source of noise in the system and/or photo bleach the fluorescent samples in the adjacent channels, particularly for the small distances between the channels found in microfluidic chips, usually in order of several micro m. We monitored this cross-talk using fluorescein as a fluorescent sample and Mylar sheeting as a microfluidic chip material. We then discuss how this cross-talk can be avoided using a simple, inexpensive and effective method.

We demonstrate an enhancement of fluorescence emission due to bimetallic silver-gold film-induced surface plasmon wave extension. Rhodamine B (RhB) dyes were excited by the evanescent wave field produced from surface plasmon polaritons excited on metal-deposited sections along an embedded strip waveguide. Various silver-gold combinations were used to quantify for the evanescent field enhancement. The underlying silver yields better evanescent field enhancement, while the overlying gold ensures that the stability of the sensing surface is not compromised. In comparison to the conventional single gold film surface plasmon resonance (SPR) configuration, the two-layered metallic structure is capable of enhancing the surface plasmon polariton (SPP) evanescent field considerably, as verified experimentally by the ca. 4.0 times improvement in the RhB fluorescence emission. The compact waveguide structure and improved electric field probing depth can potentially be exploited for on-chip SPR--fluorescence excitation of less concentrated fluorophore-labelled biological and chemical analytes, with a capability of massively parallel processing for high throughput screening.