Single-enzyme biomineralization of cadmium sulfide nanocrystals with controlled optical properties

Abstract

Nature has evolved several unique biomineralization strategies to direct the synthesis and growth of inorganic materials. These natural systems are complex, involving the interaction of multiple biomolecules to catalyze biomineralization and template growth. Herein we describe the first report to our knowledge of a single enzyme capable of both catalyzing mineralization in otherwise unreactive solution and of templating nanocrystal growth. A recombinant putative cystathionine γ-lyase (smCSE) mineralizes CdS from an aqueous cadmium acetate solution via reactive H 2 S generation from L-cysteine and controls nanocrystal growth within the quantum confined size range. The role of enzymatic nanocrystal templating is demonstrated by substituting reactive Na 2 S as the sulfur source. Whereas bulk CdS is formed in the absence of the enzyme or other capping agents, nanocrystal formation is observed when smCSE is present to control the growth. This dualfunction, single-enzyme, aerobic, and aqueous route to functional material synthesis demonstrates the powerful potential of engineered functional material biomineralization.cadmium sulfide | quantum dot | biomineralization | enzyme | nanoparticle B iological systems have evolved a diverse array of mechanisms to synthesize inorganic materials from aqueous solutions under ambient conditions. This inherent control over material properties has created interest in using these biological routes to synthesize materials (1-3) such as biosilica from sponges and diatoms (4-8), biogenic CaCO 3 from mollusks (9-12), and magnetic particles from magnetotactic bacteria (13-15). Designing a biomineralization strategy requires control of both the material composition and structure; in nature, this control is typically achieved through the assembly of a multiprotein complex, including both structuredirecting proteins and proteins responsible for mineralization of a specific composition. In the current work, we demonstrate the reduction of this complexity to its simplest form: a single enzyme capable of both catalyzing CdS mineralization and controlling particle size within the quantum confined size range to form functional biomineralized CdS quantum dots.Two of the most studied biomineralization proteins are perlucin and silicatein. Perlucin (16) has been shown to mineralize crystalline forms of CaCO 3 , a common structural material that constitutes the shell of many marine organisms, in the form of organic-inorganic composites. The role of the nacre protein perlucin in crystallite templating has been elucidated through experiments demonstrating crystallite formation in the presence of purified perlucin, and perlucin selectively being removed from solution during crystallite formation in the presence of a mixture of water-soluble, nacre-associated proteins (17). Native silicatein harvested from sea sponge or engineered forms produced recombinantly are active for biomineralization of silica and titania into structures that are amorphous or crystalline (7,18,19). In particular, biomineralizatio...

Enzymatic biomineralization of biocompatible CuInS2, (CuInZn)S2and CuInS2/ZnS core/shell nanocrystals for bioimaging

“…We have previously demonstrated this approach for non-biocompatible materials such as CdS and CdSe. 28,29 In this current work, we demonstrate the biomineralization of non-toxic, biocompatible CuInS2, (CuInZn)S2 and CuInS2/ZnS quantum dots for bioimaging applications.…”

“…24 In contrast to bio-inspired approaches that typi-cally utilize a biomolecule to template chemically induced mineralization, 25 -27 we have recently developed a single-enzyme based approach that enables direct biomineralization of aqueous stable quantum confined nanocrystals from the fewest possible components at ambient temperature. 28 Mineralization is catalyzed in otherwise inert solutions by the enzymatic turnover of the amino acid L-cysteine to form reactive H2S as a sulfur source which then reacts with metal salts in solution.…”

Single Enzyme Direct Biomineralization of CdSe and CdSe-CdS Core-Shell Quantum Dots

“…Second, the enzyme plays a role in templating the growth of the nanocrystals. 20 We term this combination "single enzyme direct biomineralization" to reflect this dual role and the active turnover of otherwise inert solutions to form these functional nanocrystals.…”

“…20 This enables direct engineering of the enzyme toward control of the key mineralization and templating processes occurring within these complex systems while achieving biomineralization with the fewest possible components, in the current case, a Cd salt, an Secontaining precursor, and the enzyme in a buff ered solution. In this specific case we also add 3-mercaptopropionic acid to stabilize the CdSe nanocrystals against photo-degradation in aqueous solution.…”

Exploiting the Potential of OLED-Based Photo-Organic Sensors for Biotechnological Applications

“…These include optically active pigments produced by photosynthetically active microorganisms [61], biomineralization products (such as quantum dots) [62] or water-polluting drugs (e.g., ibuprofen) [63], which could be detected by guest-host fluorescence amplification via the incorporation of cyclodextrin derivatives.…”