Cadmium sulphide quantum dots with tunable electronic properties by bacterial precipitation.

We present a new method to fabricate semiconducting, transition metal nanoparticles (NPs) with tunable bandgap energies using engineered Escherichia coli. These bacteria overexpress the Treponema denticola cysteine desulfhydrase gene to facilitate precipitation of cadmium sulphide (CdS) NPs. Analysis with transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy reveal that the bacterially precipitated NPs are agglomerates of mostly quantum dots, with diameters that can range from 3 to 15 nm, embedded in a carbon-rich matrix. Additionally, conditions for bacterial CdS precipitation can be tuned to produce NPs with bandgap energies that range from quantum-confined to bulk CdS. Furthermore, inducing precipitation at different stages of bacterial growth allows for control over whether the precipitation occurs intra- or extracellularly. This control can be critically important in utilizing bacterial precipitation for the environmentally-friendly fabrication of functional, electronic and catalytic materials. Notably, the measured photoelectrochemical current generated by these NPs is comparable to values reported in the literature and higher than that of synthesized chemical bath deposited CdS NPs. This suggests that bacterially precipitated CdS NPs have potential for applications ranging from photovoltaics to photocatalysis in hydrogen evolution.

Evaluation of an intervention system for parents of children with intellectual disability and challenging behaviour.

BACKGROUND: Signposts is a flexible intervention system for families of children who have intellectual disability and challenging behaviour. The Signposts materials include eight information booklets, a workbook and videotape for parents, and a series of instructional manuals for therapists. The system was designed so that it can be delivered in several different ways, i.e. group support, telephone support and self-directed modes. METHODS: The present study was an evaluation of these three modes of delivery and involved 115 families. RESULTS: Following the use of the Signposts materials in parent training programmes, the subjects reported that they were less stressed, felt more efficacious about managing their children's behaviour, were less hassled about meeting their own needs and that their children's behaviour had improved. Additionally, families generally reported high levels of satisfaction with the content and delivery of the materials. CONCLUSIONS: Finally, there were minimal differences among the three modes of delivery on the measures used, although families who used the self-directed mode were less likely to complete the materials. Implications of these results for service delivery are discussed.