Microwave-assisted Aqueous Synthesis Of CdTe Semiconductor Nanocrystals And Application In Fingerprint Detection

Highly fluorescence semiconductor nanocrystals have wide applications in optoelectronic conversion, sensor, optical display, and especially biological imaging ,which have attracted considerable interest. As luminescent probes, semiconductor nanocrystals present considerable advantages over conventional organic dye molecules. However, luminescent nanocrystals are commonly prepared by organometallic procedure and not compatible with aqueous assay conditions. Consequently, it is necessary to substitute the surface organic ligands with hydrophilic capping agents for biological applications. But for these methods, the conditions of preparation of nanocrystals were relatively critical, and the process was complicated. In contrast, the synthesis method of nanocrystals in an aqueous medium using thiols as stabilizing agents is of simplicity, low toxicity and low cost. Most important is that the stability of nanocrystals synthesized by aqueous approach is better than that of the water-soluble nanocrystals transformed from organic solvent. This thesis attempted to synthesize a water-soluble cadmium tellurium (CdTe) nanocrytal by microwave irradiation and use it in latent fingerprint detection.In Chapter 1, the basic properties and unique optical properties of semiconductor nanocrystals are introduced. The synthesis methods of nanocrystals are summarized. The development and the trends of the nanocrystals are specially introduced.The methods on latent fingerprint detection are reviewed.In Chapter 2, CdTe nanoparticles were synthesized in aqueous solution using different modes of microwave reactor. The X-ray powder diffraction, transmission electron microscopy, ultraviolet spectrometry and fluorescence spectrometry were used to analyze the composite nanocrystals and determine their average size, size distribution, shape, internal structure and elemental composition. CdTe nanoparticles with high fluorescence quantum yield (28%) were synthesized in aqueous solution. These nanoparticles can be coupled with amido by the outer carboxyl group for fingerprint detection.In Chapter 3, CdTe nanoparticles were used in latent fingerprint detection .It simply involved spraying the CdTe solution on the articles and then fumed cyanoacrylate ester . We placed sample fingerprints on aluminum foil, glass slide, beverage bottle and coated paper, then used concentric pneumatic nebulizer or ultrasonic nebulizer to spray the NCs on the articles, using the carboxyl group in CdTe nanoparticles coupled with the amido in fingerprint for detection.Spotted portions of fingerprints revealed amply intense luminescence whereas the corresponding unspotted portions generally had washed-out detail with weaker fluorescence, the fingerprint was easily visible. The fingerprints can maintain high PL intensity for more than several months in the air and room temperature.