Non-emissive plastic colour filters for fluorescence detection.

We report the fabrication of non-emissive short- and long-pass filters on plastic for high sensitivity fluorescence detection. The filters were prepared by overnight immersion of titania-coated polyethylene terephthalate (PET) in an appropriate dye solution - xylene cyanol for short-pass filtering and fluorescein disodium salt for long-pass filtering - followed by repeated washing to remove excess dye. The interface between the titania and the dye molecule induces efficient quenching of photo-generated excitons in the dye molecule, reducing auto-fluorescence to negligible values and so overcoming the principal weakness of conventional colour filters. Using the filters in conjunction with a 505 nm cyan light-emitting diode and a Si photodiode, dose-response measurements were made for T8661 Transfluosphere beads in the concentration range 1 × 10(9) to 1 × 10(5) beads µL(-1), yielding a limit of detection of 3 × 10(4) beads µL(-1). The LED/short-pass filter/T8661/long-pass filter/Si-photodiode combination reported here offers an attractive solution for sensitive, low cost fluorescence detection that is readily applicable to a wide range of bead-based immunodiagnostic assays.

A stable droplet reactor for high temperature nanocrystal synthesis.

We report a versatile capillary-based droplet reactor for the controlled synthesis of nanoparticles over a wide range of flow conditions and temperatures. The reactor tolerates large flow-rate differentials between individual reagent streams, and allows droplet composition to be varied independently of residence time and volume. The reactor was successfully applied to the synthesis of metal (Ag), metal-oxide (TiO(2)) and compound semiconductor (CdSe) nanoparticles, and in each case exhibited stable droplet flow over many hours of operation without fouling, even for reactions involving solid intermediates. For CdSe formed by the reaction of Cd oleate and Se, highly controlled growth could be achieved at temperatures of up to 250 °C, with emission spectra varying smoothly and reproducibly with temperature and flow-rate. The droplet reactor showed exceptional stability when operated under constant flow-rate and temperature conditions, yielding particles with well-defined band-edge emission spectra that did not vary over the course of a full day's continuous operation.

Intelligent routes to the controlled synthesis of nanoparticles.

We describe an autonomous 'black-box' system for the controlled synthesis of fluorescent nanoparticles. The system uses a microfluidic reactor to carry out the synthesis and an in-line spectrometer to monitor the emission spectra of the emergent particles. The acquired data is fed into a control algorithm which reduces each spectrum to a scalar 'dissatisfaction coefficient' and then intelligently updates the reaction conditions in an effort to minimise this coefficient and so drive the system towards a desired goal. In the tests reported here, CdSe nanoparticles were prepared by separately injecting solutions of CdO and Se into the two inlets of a heated y-shaped microfluidic reactor. A noise-tolerant global search algorithm was then used to efficiently identify-without any human intervention-the injection rates and temperature that yielded the optimum intensity for a chosen emission wavelength.