Single-pot biofabrication of zinc sulfide immuno-quantum dots

Formation of CdTe core and CdTe@ZnTe core-shell quantum dots via hydrothermal approach using dual capping agents: deciphering the food dye sensing and protein binding applications

Excessive use of food coloring agents in the food industry to make the food more attractive or improve the taste has caused various health and ecological problems. Therefore, it is necessary to develop a reliable, sensitive, and selective sensing probe to detect food dyes in different food products for future industrial processing and biosafety. In recent decades, surface-functionalized quantum dots (QDs), owing to their unique optical properties, have gained tremendous interest for a wide range of applications, including biomedical, bioimaging and sensing applications. Herein, we have reported the synthesis of excellent colloidal stable and highly luminescent CdTe core and CdTe@ZnTe core-shell QDs using dual functionalizing agents, polyvinyl pyrrolidone and vitamin C. The synthesized QDs were explored as excellent sensing probes for the food dyes carmoisine, Ponceau 4R and tartrazine with limit of detection (LOD) values of 0.097 ± 0.006, 0.147 ± 0.001 and 0.044 ± 0.001 μM for CdTe-PVP QDs and 0.079 ± 0.001, 0.114 ± 0.002 and 0.042 ± 0.001 μM for CdTe@ZnTe-PVP QDs, respectively. The sensitivity of the synthesized QDs for the food dyes was also investigated in real samples (soft drinks and medications). Moreover, considering the potential effects of QDs as therapeutics or nano-drug carriers, the interactions between the synthesized QDs and carrier protein human serum albumin (HSA) were investigated. The binding affinity was observed to be in the order of 104 M-1. QDs were found to quench the intrinsic fluorescence of HSA, and both types of quenching (static and dynamic) occur via electrostatic interactions in association with hydrophobic forces without any significant alteration in the protein structure.

Formation of ZnS quantum dots using green tea extract: applications to protein binding, bio-sensing, anti-bacterial and cell cytotoxicity studies

Biocompatible quantum dots (QDs) have attracted a lot of attention due to their potential biological applications (drug delivery, sensing and diagnosis). Here, we have synthesized 2-4 nm sized biocompatible zinc sulphide (ZnS) QDs using a plant leaf extract as an immobilizing and stabilizing agent via a green route. We have investigated the biological effects of ZnS QDs in a variety of applications, including (1) anti-bacterial activity, (2) cell cytotoxicity, (3) bio-sensing and (4) protein binding. Studies on the anti-bacterial activity of the as-synthesized ZnS QDs against E. coli and E. faecalis inhibited bacterial growth effectively and showed a cytotoxic effect on the HeLa cell line. The biosynthesized ZnS QDs act as a fluorescence probe to detect bilirubin and rifampicin (RFP) with a wide linear range, high sensitivity, good selectivity, and a low limit of detection (LOD), with LOD values of 22.12 ± 0.25 ng mL^-1 and 122.37 ± 0.42 ng mL^-1, respectively. In a biological matrix, the QDs can form a complex with biomacromolecules; therefore, we studied the interaction between a carrier protein (HSA) and the as-synthesized ZnS QDs. The surface functionalized and nano-sized ZnS-GT QDs were observed to form complexes with the human serum albumin (HSA) protein and quenched the intrinsic fluorescence of HSA through static and dynamic quenching modes. The binding affinity was observed to be of the order of 10⁵ M^-1 for the HSA-ZnS-GT QD interactions, which can be considered as a reversible mode of binding. The effect of the ZnS QDs on other ligands and protein interactions was also studied. Enhanced binding affinities for HSA-quercetin ((5.994 ± 0.139) × 10⁵ M^-1) and HSA-luteolin ((3.068 ± 0.127) × 10⁵ M^-1) interactions were also observed in the presence of ZnS-GT QDs.

Achieving regioselective materials binding using multidomain peptides

The ability to integrate two disparate materials-binding domains into a single ligand to achieve regiospecific binding would be powerful to direct material assembly; however, this has proven challenging to achieve due to cross-materials binding. Accomplishing this goal might be achieved by harnessing the precision of biology to exploit the recognition between peptides and specific nanomaterials. Here, a designed bifunctional molecule termed Biomolecular Exfoliant and Assembly Motifs (BEAM) is introduced, featuring two different materials-binding peptide domains, one for graphene and one for hexagonal boron nitride (h-BN), at each end of the molecule, separated by a fatty acid spacer. The BEAM is demonstrated to bind strongly to both graphene and h-BN surfaces, and in each case the materials-binding peptide domain is shown to preferentially bind its target material. Critically, the two materials-binding domains exhibited limited cross-domain interaction. The BEAM design concept shows substantial potential to eventually guide self-organization of a range of materials in aqueous media.

Different metal-doped ZnS quantum dots photocatalysts for enhancing the permeability and antifouling performances of polysulfone membranes with and without UV irradiation

In this study, the effect of three different transition metal ion dopants (Mn²⁺, Fe^2+, and Co²⁺) on the characteristics of zinc sulfide (ZnS) quantum dots (QDs) was investigated and the obtained QDs photocatalysts were applied for the modification of polysulfone (PSf) mixed matrix membranes to reduce membrane fouling. The synthesized QDs and fabricated membranes were fully identified with SEM, TEM, AFM, FTIR analyses, and also underwent porosity and contact angle tests. Flux recovery ratios (FRR) significantly increased from 69.8% (bare) to 85.0% (1% Fe-doped ZnS QDs) after modification of membranes with metal-doped QDs. The contact angles of the prepared membranes decreased with doping of dissimilar metals, therefore hydrophilicity increased, and reversible/non-reversible blockages were improved. Besides, the use of UV irradiation during the washing of the membranes increased the FRR of the photocatalytic activated membranes to 91.2%. Compared to the bare PSf membrane in dye solution filtration, 1% Fe-doped ZnS QDs membrane yielded twice as much flux and 15% higher FRR results. Therefore, the results proved that metal-doped QDs can be used in the modification of PSf membranes with high efficiency.

Structure-guided identification of a peptide for bio-enabled gold nanoparticle synthesis

In this study, we show that maltose-binding protein (MBP) is capable of facilitating stable gold nanoparticle synthesis, and a structure of MBP in the presence of gold ions was determined by X-ray crystallography. Using this high-resolution structure of gold ion bound MBP, a peptide (AT1) was selected and synthesized and was shown to also aid in the synthesis of stable gold nanoparticles under similar experimental conditions to those used for protein facilitated synthesis. This structure-based approach represents a new potential method for the selection of peptides capable of facilitating stable nanoparticle synthesis.

Synthetic Genetic Circuits for Self-Actuated Cellular Nanomaterial Fabrication Devices

Genetically controlled synthetic biosystems are being developed to create nanoscale materials. These biosystems are modeled on the natural ability of living cells to synthesize materials: many organisms have dedicated proteins that synthesize a wide range of hard tissues and solid materials, such as nanomagnets and biosilica. We designed an autonomous living material synthesizing system consisting of engineered cells with genetic circuits that synthesize nanomaterials. The circuits encode a nanomaterial precursor-sensing module (sensor) coupled with a materials synthesis module. The sensor detects the presence of cadmium, gold, or iron ions, and this detection triggers the synthesis of the related nanomaterial-nucleating extracellular matrix. We demonstrate that when engineered cells sense the availability of a precursor ion, they express the corresponding extracellular matrix to form the nanomaterials. This proof-of-concept study shows that endowing cells with synthetic genetic circuits enables nanomaterial synthesis and has the potential to be extended to the synthesis of a variety of nanomaterials and biomaterials using a green approach.

Determination of conjugated protein on nanoparticles by an adaptation of the Coomassie blue dye method

A new accurate spectrophotometric method for protein determination on nanoparticles is described. The method is based on the Coomassie blue dye that binds to the basic and aromatic amino acid residues of proteins, especially arginine and lysine. A known amount of reagent dye was mixed with a variety of protein-loaded nanoparticles. Thereafter the unconjugated reagent was mixed with excess protein (bovine serum albumin) and titrated. In this method, the reacted dye on the protein coating of nanoparticle is directly determined, in opposite to the conventional method, in which the conjugated protein is determined as the difference between the non-conjugated protein found in the supernatant after centrifugation, and the total amount of protein originally used. This method is able to measure amounts of coated protein lower than 1 ppm.

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Simple and accurate method especially adapted for protein-coated nanoparticles.

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The amino acid residues of protein in the nanoparticle surface react with Coomassie brilliant blue dye.

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The unreacted dye is titrated with an excess of a standard protein.

Low temperature aqueous synthesis of size-controlled nanocrystals through size focusing: a quantum dot biomineralization case study

Traditional quantum dot synthesis techniques rely on the separation of nucleation and growth to control nanocrystal size. However, the same goal can be achieved through slow and continuous introduction of reactive precursors to keep the growth mechanism in the size focusing regime throughout synthesis. In this work, we demonstrate the efficacy of this approach within the framework of functional material biomineralization where, despite simultaneous nucleation and growth of particles, this growth mechanism enables size-controlled nanocrystal synthesis. Herein, the single enzyme cystathionine γ-lyase (CSE) is utilized to biomineralize CdS nanocrystals via the slow, but continuous turnover of the amino acid l-cysteine to produce H2S. Nanocrystal nucleation and growth theories confirm that consistent addition of monomers will result in a high supersaturation term, driving the nanocrystal growth mechanism into the size focusing regime. We further confirm this theory by mimicking biomineralization via chemical routes and demonstrate the influence of varying supersaturation, to further control the average nanocrystal size. Finally, altering the chelation strength of the capping agent l-cysteine is found to play a key role in balancing nanocrystal growth in solution and long-term stability.

Synthetic biology engineering of biofilms as nanomaterials factories

Bottom-up fabrication of nanoscale materials has been a significant focus in materials science for expanding our technological frontiers. This assembly concept, however, is old news to biology — all living organisms fabricate themselves using bottom-up principles through a vast self-organizing system of incredibly complex biomolecules, a marvelous dynamic that we are still attempting to unravel. Can we use what we have gleaned from biology thus far to illuminate alternative strategies for designer nanomaterial manufacturing? In the present review article, new synthetic biology efforts toward using bacterial biofilms as platforms for the synthesis and secretion of programmable nanomaterials are described. Particular focus is given to self-assembling functional amyloids found in bacterial biofilms as re-engineerable modular nanomolecular components. Potential applications and existing challenges for this technology are also explored. This novel approach for repurposing biofilm systems will enable future technologies for using engineered living systems to grow artificial nanomaterials.

Streamlined Synthesis and Assembly of a Hybrid Sensing Architecture with Solid Binding Proteins and Click Chemistry

Combining bioorthogonal chemistry with the use of proteins engineered with adhesive and morphogenetic solid-binding peptides is a promising route for synthesizing hybrid materials with the economy and efficiency of living systems. Using optical sensing of chloramphenicol as a proof of concept, we show here that a GFP variant engineered with zinc sulfide and silica-binding peptides on opposite sides of its β-barrel supports the fabrication of protein-capped ZnS:Mn nanocrystals that exhibit the combined emission signatures of organic and inorganic fluorophores. Conjugation of a chloramphenicol-specific DNA aptamer to the protein shell through strain-promoted azide-alkyne cycloaddition and spontaneous concentration of the resulting nanostructures onto SiO₂ particles mediated by the silica-binding sequence enables visual detection of environmentally and clinically relevant concentrations of chloramphenicol through analyte-mediated inner filtering of sub-330 nm excitation light.

Solid-Binding Peptides in Biomedicine

Some peptides are able to bind to inorganic materials such as silica and gold. Over the past decade, Solid-binding peptides (SBPs) have been used increasingly as molecular building blocks in nanobiotechnology. These peptides show selectivity and bind with high affinity to a diverse range of inorganic surfaces e.g. metals, metal oxides, metal compounds, magnetic materials, semiconductors, carbon materials, polymers and minerals. They can be used in applications such as protein purification and synthesis, assembly and the functionalization of nanomaterials. They offer simple and versatile bioconjugation methods that can increase biocompatibility and also direct the immobilization and orientation of nanoscale entities onto solid supports without impeding their functionality. SBPs have been employed in numerous nanobiotechnological applications such as the controlled synthesis of nanomaterials and nanostructures, formation of hybrid biomaterials, immobilization of functional proteins and improved nanomaterial biocompatibility. With advances in nanotechnology, a multitude of novel nanomaterials have been designed and synthesized for diagnostic and therapeutic applications. New approaches have been developed recently to exert a greater control over bioconjugation and eventually, over the optimal and functional display of biomolecules on the surfaces of many types of solid materials. In this chapter we describe SBPs and highlight some selected examples of their potential applications in biomedicine.

Organic crystal-binding peptides: morphology control and one-pot formation of protein-displaying organic crystals

Crystalline assemblies of fluorescent molecules have different functional properties than the constituent monomers, as well as unique optical characteristics that depend on the structure, size, and morphological homogeneity of the crystal particles. In this study, we selected peptides with affinity for the surface of perylene crystal particles by exposing a peptide-displaying phage library in aqueous solution to perylene crystals, eluting the surface-bound phages by means of acidic desorption or liquid-liquid extraction, and amplifying the obtained phages in Escherichia coli. One of the perylene-binding peptides, PeryBPb1: VQHNTKYSVVIR, selected by this biopanning procedure induced perylene molecules to form homogenous planar crystal nanoparticles by means of a poor solvent method, and fusion of the peptide to a fluorescent protein enabled one-pot formation of protein-immobilized crystalline nanoparticles. The nanoparticles were well-dispersed in aqueous solution, and Förster resonance energy transfer from the perylene crystals to the fluorescent protein was observed. Our results show that the crystal-binding peptide could be used for simultaneous control of perylene crystal morphology and dispersion and protein immobilization on the crystals.

A minimized designer protein for facile biofabrication of ZnS:Mn immuno-quantum dots

A minimized protein consisting of a linear ZnS-binding peptide fused to an antibody-binding domain supports the one-step aqueous synthesis of Mn-doped ZnS nanocrystals that exhibit smaller size, brighter fluorescence and improved antibody-binding relative to those made with the original designer protein.

Glucose oxidase-directed, instant synthesis of Mn-doped ZnS quantum dots in neutral media with retained enzymatic activity: mechanistic study and biosensing application

Protein-directed synthesis of quantum dots (QDs) is a "greener" alternative to the current high-temperature and aqueous synthetic protocols, which provide water-soluble, biocompatible protein-functionalized QDs in one-pot. However, the protein activity in such synthetic schemes is a critical issue, since the synthetic conditions (for instance, high pH of the precursors, long time of synthesis, and disruption of disulfide bonds) are not suitable for retaining the activity (especially for enzymes). Herein, we present a facile and instant glucose oxidase (GOD)-directed strategy for the preparation of highly luminescent, phosphorescent Mn-doped ZnS (Mn-ZnS) QDs in one-step at room temperature and in neutral aqueous media. With such mild synthetic conditions, the enzymatic activity of GOD was totally retained. Furthermore, we also carried out GOD-directed synthesis of QDs with several other conditions that are reported in the literature. It turned out that the GOD enzymatic activity under these synthetic conditions was lower than that of the proposed protocol, indicating that mild synthetic conditions are the prerequisite for retaining the enzymatic activity. Importantly, the as-prepared GOD-mediated Mn-ZnS QDs exhibited high photostability, high salt tolerance and colloidal stability, and can be stored for months at 4 °C or 25 °C without changing their phosphorescent intensity and enzymatic activity. Via selective chemical modification, the exact functional groups (amino acid residues) of GOD in directing the synthesis of Mn-ZnS QDs were studied in detail. It turned out to be imidazole in histidine residues but not thiol in cysteine residues that directed the formation of Mn-ZnS QDs, and this was further confirmed with several other proteins for synthesis of Mn-ZnS QDs. The as-prepared GOD-capped Mn-ZnS QDs were employed as phosphorescent probes for background-free sensing of glucose in serum samples.

Microbial Uptake, Toxicity, and Fate of Biofabricated ZnS:Mn Nanocrystals

Despite their importance in nano-environmental health and safety, interactions between engineered nanomaterials and microbial life remain poorly characterized. Here, we used the model organism E. coli to study the penetration requirements, subcellular localization, induction of stress responses, and long-term fate of luminescent Mn-doped ZnS nanocrystals fabricated under "green" processing conditions with a minimized ZnS-binding protein. We find that such protein-coated quantum dots (QDs) are unable to penetrate the envelope of unmodified E. coli but readily translocate to the cytoplasm of cells that have been made competent by chemical treatment. The process is dose-dependent and reminiscent of bacterial transformation. Cells that have internalized up to 0.5 μg/mL of nanocrystals do not experience a significant activation of the unfolded protein or SOS responses but undergo oxidative stress when exposed to high QD doses (2.5 μg/mL). Finally, although they are stable in quiescent cells over temperatures ranging from 4 to 42°C, internalized QDs are rapidly diluted by cell division in a process that does not involve TolC-dependent efflux. Taken together, our results suggest that biomimetic QDs based on low toxicity inorganic cores capped by a protein shell are unlikely to cause significant damage to the microbial ecosystem.

Solid-binding peptides: smart tools for nanobiotechnology

Over the past decade, solid-binding peptides (SBPs) have been used increasingly as molecular building blocks in nanobiotechnology. These peptides show selectivity and bind with high affinity to the surfaces of a diverse range of solid materials including metals, metal oxides, metal compounds, magnetic materials, semiconductors, carbon materials, polymers, and minerals. They can direct the assembly and functionalisation of materials, and have the ability to mediate the synthesis and construction of nanoparticles and complex nanostructures. As the availability of newly synthesised nanomaterials expands rapidly, so too do the potential applications for SBPs.

Biofabrication of ZnS:Mn luminescent nanocrystals using histidine, hexahistidine, and His-tagged proteins: a comparison study

The ubiquitous hexahistidine purification tag has been used to conjugate proteins to the shell of CdSe:ZnS quantum dots (QDs) due to its affinity for surface-exposed Zn²⁺ ions but little attention has been paid to the potential of His-tagged proteins for mineralizing luminescent ZnS nanocrystals. Here, we compare the ability of free histidine, a His tag peptide, His-tagged thioredoxin (TrxA, a monomeric protein), and N- and C-terminally His-tagged versions of Hsp31 (a homodimeric protein) to support the synthesis of Mn-doped ZnS nanocrystals from aqueous precursors under mild conditions of pH (8.2) and temperature (37°C). We find that: (1) it is possible to produce poor quality QDs when histidine is used at high (8 mM) concentration; (2) an increase in local histidine concentration through repetition of the amino acid as a His tag decreases the amount of needed reagent ≈10-fold and improves optical properties; (3) fusion of the same His tag to TrxA allows for ZnS:Mn QDs mineralization at micromolar concentrations; and (4) doubling the local hexahistidine concentration by exploiting Hsp31 dimerization further improves nanocrystal luminescence with the brightest particles obtained when His tags are spatially co-localized at the Hsp31 N-termini. Although hexahistidine tracts are not as efficient as combinatorially selected ZnS binding peptides at QD synthesis, it should be possible to use the large number of available His-tagged proteins and the synthesis approach described herein to produce luminescent nanoparticles whose protein shell carries a broad range of functions.

Enzymatic fabrication of protein-decorated gold nanoparticles by the aid of artificial peptides with gold-binding affinity

Here, we report a new approach for the biofabrication of protein-immobilized gold nanoparticles (Au NPs), using oxidoreductase with gold-binding peptide-tagged recombinant proteins. The reduction of Au ions to Au(0) was achieved using a natural electron-donating cofactor, nicotinamide adenine dinucleotide, which was regenerated by the glycerol dehydrogenase (GLD) enzyme. First, we selected the A3 peptide (AYSSGAPPMPPF) as a gold binding moiety. The A3 peptide was introduced to the C-terminus of fusion proteins of immunoglobulin G (IgG)-binding domains of protein G and protein A. In the presence of the recombinant protein, the GLD-catalyzed cofactor reduction resulted in the efficient in situ fabrication of Au NPs immobilized with the fusion protein. Moreover, the protein-immobilized Au NPs were shown to have IgG binding activity. Although the A3 peptide had the ability to stabilize Au NPs, the results suggested that its binding affinity for Au NPs was unexpectedly weaker than that of His-tag. A cysteine residue was thus introduced to a recombinant protein adjacent to the A3 peptide. Finally, an artificial peptide, comprising A3 sequence with the C-terminal single cysteine residue, enabled the stable display of a fusion protein while maintaining its IgG binding activity through the Au-S bond. This enzyme-assisted one-pot methodology for protein-Au NPs conjugation offers one potent route for the facile fabrication of biomolecule-decorated metal NPs.

Just-in-time vaccines: Biomineralized calcium phosphate core-immunogen shell nanoparticles induce long-lasting CD8(+) T cell responses in mice

Distributed and on-demand vaccine production could be game-changing for infectious disease treatment in the developing world by providing new therapeutic opportunities and breaking the refrigeration "cold chain". Here, we show that a fusion protein between a calcium phosphate binding domain and the model antigen ovalbumin can mineralize a biocompatible adjuvant in a single step. The resulting 50 nm calcium phosphate core-immunogen shell particles are comparable to soluble protein in inducing ovalbumin-specific antibody response and class switch recombination in mice. However, single dose vaccination with nanoparticles leads to higher expansion of ovalbumin-specific CD8(+) T cells upon challenge with an influenza virus bearing the ovalbumin-derived SIINFEKL peptide, and these cells produce high levels of IFN-γ. Furthermore, mice exhibit a robust antigen-specific CD8(+) T cell recall response when challenged with virus 8 months post-immunization. These results underscore the promise of immunogen-controlled adjuvant mineralization for just-in-time manufacturing of effective T cell vaccines.

FROM THE CLINICAL EDITOR

This paper reports that a fusion protein between a calcium phosphate binding domain and the model antigen ovalbumin can mineralize into a biocompatible adjuvant in a single step, enabling distributed and on-demand vaccine production and eliminating the need for refrigeration of vaccines. The findings highlight the possibility of immunogen-controlled adjuvant mineralization for just-in-time manufacturing of effective T cell vaccines.

Carbon-binding designer proteins that discriminate between sp2- and sp3-hybridized carbon surfaces

Robust and simple strategies to directly functionalize graphene- and diamond-based nanostructures with proteins are of considerable interest for biologically-driven manufacturing, biosensing, and bioimaging. Here, we identify a new set of carbon-binding peptides that vary in overall hydrophobicity and charge and engineer two of these sequences (Car9 and Car15) within the framework of E. coli thioredoxin 1 (TrxA). We develop purification schemes to recover the resulting TrxA derivatives in a soluble form and conduct a detailed analysis of the mechanisms that underpin the interaction of the fusion proteins with carbonaceous surfaces. Although equilibrium quartz crystal microbalance measurements show that TrxA::Car9 and TrxA::Car15 have similar affinities for sp(2)-hybridized graphitic carbon (Kd = 50 and 90 nM, respectively), only the latter protein is capable of dispersing carbon nanotubes. Further investigation by surface plasmon resonance and atomic force microscopy reveals that TrxA::Car15 interacts with sp(2)-bonded carbon through a combination of hydrophobic and π-π interactions but that TrxA::Car9 exhibits a cooperative mode of binding that relies on a combination of electrostatics and weaker π stacking. Consequently, we find that TrxA::Car9 binds equally well to sp(2)- and sp(3)-bonded (diamondlike) carbon particles whereas TrxA::Car15 is capable of discriminating between the two carbon allotropes. Our results emphasize the importance of understanding both bulk and molecular recognition events when exploiting the adhesive properties of solid-binding peptides and proteins in technological applications.

A high-affinity gold-binding camel antibody: antibody engineering for one-pot functionalization of gold nanoparticles as biointerface molecules

Antibodies, with their high affinity and specificity, are widely utilized in the field of protein engineering, medicinal chemistry, and nanotechnology applications, and our recent studies have demonstrated the recognition and binding of antibody for the surface on inorganic material. In this study, we generated a high-affinity gold-binding antibody fragment by a combination of peptide-grafting and phage-display techniques and showed the availability of the material-binding fragment for one-pot functionalization of nanoparticles as interface molecules. After a gold-binding peptide sequence was grafted into one of the complementarity determining regions of a single variable domain of a heavy-chain camel antibody, a combinatorial library approach raised by 20 times the affinity of the peptide-grafted fragment. The high-affinity gold-binding fragment (E32) spontaneously adsorbed on gold nanoparticles, and consequently the nanoparticles formed a stable dispersion in a high-ionic-strength solution. Multivalent and bispecific antibodies constructed on the E32 platform by means of fusion technology functionalized gold nanoparticles in one pot, and these functionalized nanoparticles could be used to obtain surface plasmon resonance scattering images of cancer cells and to spontaneously link two different nanomaterials. Here, we propose the bispecific antibodies as convenient interface molecules in the nanosized world.

Facile, rapid and efficient biofabrication of gold nanoparticles decorated with functional proteins

We report a one-pot biological approach to fabricate gold nanoparticle (AuNP)-ZZ domain conjugates using peptide-functionalized proteins that can simultaneously direct both biomineralization and surface modification of AuNPs. In addition, immuno-AuNPs are readily prepared through the specific binding of antibodies to the ZZ domain on the AuNPs.

Facile synthesis of fluorescent porous zinc sulfide nanospheres and their application for potential drug delivery and live cell imaging

Fabrication of intrinsically fluorescent porous nanocarriers that are simultaneously stable in aqueous solutions and photostable is critical for their application in drug delivery and optical imaging but remains a challenge. In this study, fluorescent porous zinc sulfide nanospheres were synthesized by a facile gum arabic-assisted hydrothermal procedure. The morphology, composition and properties of the nanospheres have been characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, N(2) adsorption-desorption analysis, thermal gravimetric analysis, fourier transform infrared spectrograph, optical measurement, dynamic light scattering, and cytotoxicity assay. They exhibit larger surface area, excellent colloidal stability, photostable fluorescent signals, and good biocompatibility, which makes them promising hosts for drug delivery and cellular imaging. The fluorescent dye safranine-T was employed as a drug model and loaded into the porous nanospheres, which were delivered to human cervical cancer HeLa cells in vitro for live cell imaging.

Effect of solid surface charge on the binding behaviour of a metal-binding peptide

Over the last decade, solid-binding peptides have been increasingly used as molecular building blocks coupling bio- and nanotechnology. Despite considerable research being invested in this field, the effects of many surface-related parameters that define the binding of peptide to solids are still unknown. In the quest to control biological molecules at solid interfaces and, thereby, tailoring the binding characteristics of the peptides, the use of surface charge of the solid surface may probably play an important role, which then can be used as a potential tuning parameter of peptide adsorption. Here, we report quantitative investigation on the viscoelastic properties and binding kinetics of an engineered gold-binding peptide, 3RGBP(1), adsorbed onto the gold surface at different surface charge densities. The experiments were performed in aqueous solutions using an electrochemical dissipative quartz crystal microbalance system. Hydrodynamic mass, hydration state and surface coverage of the adsorbed peptide films were determined as a function of surface charge density of the gold metal substrate. Under each charged condition, binding of 3rGBP(1) displayed quantitative differences in terms of adsorbed peptide amount, surface coverage ratio and hydration state. Based on the intrinsically disordered structure of the peptide, we propose a possible mechanism for binding of the peptide that can be used for tuning surface adsorption in further studies. Controlled alteration of peptide binding on solid surfaces, as shown here, may provide novel methods for surface functionalization used for bioenabled processing and fabrication of future micro- and nanodevices.

Laying out ground rules for protein-aided nanofabrication: ZnO synthesis at 70°C as a case study

Designer proteins that incorporate solid-binding peptides hold promise to control the nucleation, growth, morphology, and assembly of inorganic phases under mild conditions of temperature and pressure. However, protein-aided nanofabrication remains more art than science and some materials can only be synthesized at temperatures that cause most mesophilic proteins to unfold. Using zinc oxide (ZnO) synthesis at 70°C as case study, we show here that seemingly unimportant variables, such as the carry-over concentration of Tris buffer and the "empty" host protein scaffold can exert a significant influence on materials morphology. We also show that, once well-controlled conditions are established, thermodynamic predictions and adsorption isotherms are powerful tools to understand how various ZnO-binding sequence inserted within the thermostable framework of Escherichia coli thioredoxin A (TrxA) affect inorganic morphogenesis.

Biomineralization and size control of stable calcium phosphate core-protein shell nanoparticles: potential for vaccine applications

Calcium phosphate (CaP) polymorphs are nontoxic, biocompatible and hold promise in applications ranging from hard tissue regeneration to drug delivery and vaccine design. Yet, simple and robust routes for the synthesis of protein-coated CaP nanoparticles in the sub-100 nm size range remain elusive. Here, we used cell surface display to identify disulfide-constrained CaP binding peptides that, when inserted within the active site loop of Escherichia coli thioredoxin 1 (TrxA), readily and reproducibly drive the production of nanoparticles that are 50-70 nm in hydrodynamic diameter and consist of an approximately 25 nm amorphous calcium phosphate (ACP) core stabilized by the protein shell. Like bone and enamel proteins implicated in biological apatite formation, peptides supporting nanoparticle production were acidic. They also required presentation in a loop for high-affinity ACP binding as elimination of the disulfide bridge caused a nearly 3-fold increase in hydrodynamic diameters. When compared to a commercial aluminum phosphate adjuvant, the small core-shell assemblies led to a 3-fold increase in mice anti-TrxA titers 3 weeks postinjection, suggesting that they might be useful vehicles for adjuvanted antigen delivery to dendritic cells.

Aqueous, protein-driven synthesis of transition metal-doped ZnS immuno-quantum dots

The intentional introduction of transition metal impurities in semiconductor nanocrystals is an attractive approach for tuning quantum dot emission over a wide range of wavelengths. However, the development of effective doping strategies can be challenging, especially if one simultaneously requires a low-toxicity crystalline core, a functional protein shell, and a "green", single-step synthesis process. Here, we describe a simple and environmentally friendly route for the biofabrication of Cu-doped (blue-green) or Mn-doped (yellow-orange) ZnS nanocrystals surrounded by an antibody-binding protein shell. The ZnS:Mn hybrid particles obtained with this method exhibit a 60% enhancement in maximum photoluminescence intensity relative to undoped nanocrystals and have a hydrodynamic diameter inferior to 10 nm. They can be stored for months at 4 °C, are stable over a physiological range of pH and salt concentrations, can be decorated with variable amounts of antibodies by direct mixing, and hold promise for biosensing and imaging applications.

Fabrication of ordered nanostructures of sulfide nanocrystal assemblies over self-assembled genetically engineered P22 coat protein

Ordered ZnS and CdS nanocrystal assemblies have been synthesized by a facile bioinspired approach consisting of an initial self-assembly of engineered proteins into spherical biotemplates and a subsequent protein-directed nucleation and growth of ZnS and CdS nanocrystals symmetrically distributed over the self-assembled biotemplates.