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Cadmium sulfide nanoparticles (3.2 to 5.6 nm) are synthesized using R-phycoerythrin as a protein matrix. The effects of the reactant concentrations and solution pH on the particle size of CdS are examined. The optical and photochemical properties of the nanoparticles are studied. Selective fluorimetry results suggest that CdS particles ≥ 3.2 nm in diameter are heteroaggregates. It is found that, during photoreduction of methyl viologen dichloride, the synthesis of CdS nanoparticles resumes. The growth of CdS particles is presumably restricted by the dimensions of the channel in the center of the R-phycoerythrin hexamer (3.5 × 6 nm).

As evidenced by ion-selective electrode potentiometry, the hexameric R -phycoerythrin (RPE) molecule binds 20-4000 cadmium ions (Cd 2+ ) depending on Cd 2+ concentration in the solution. Cadmium ions bound to RPE serve as the nuclei of cadmium sulfide crystallization in the presence of sulfide ions. According to spectrometric, electron-microscopic, and capillary electrophoresis data, the particles are heteroaggregates of 3.2 × 6 nm in size. The fact that the particle size fits the size of the central tunnel of the RPE molecule and the similarity between the electrophoretic patterns of free RPE and the RPE-CdS complex indicate that the tunnel space, limiting the crystal growth, is the most probable site of nanoparticle formation. Properties of the nanoparticles can be modified by changing temperature, pH, etc. It is concluded that RPE can be used as a reagent for detoxification of cadmium ions and a matrix for synthesis of elongated CdS nanoparticles.

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