Currently, protein/peptide-based biomimetic mineralization has been demonstrated to be an efficient and promising strategy for synthesis of inorganic/metal nanoparticles (NPs) for bioapplications. This strategy is found to be bio-inspired, straightforward, and environmentally benign. It can produce inorganic/metal NPs with good stability, excellent biocompatibility, high water solubility, and rich surface functional groups for further bioconjunction. In this review, we provide a summary of the previously reported proteins/peptides as biotemplates involved in biomimetic mineralization synthesis, and categorize the obtained inorganic NPs ranging from metal nanoclusters (MNCs), quantum dots (QDs), gadolinium derivatives, and metal sulfide nanoparticles (MSNPs) with an emphasis on the recent progress in their use in biomedical applications, including bio-sensing, ion detection, bio-labeling, in vivo imaging and therapy. In the end, the challenges and future outlook in this emerging area are also discussed.

Glioma stem cells (GSCs) are considered the key to the occurrence, development, invasion, recurrence and sensitivity to treatment of brain tumors. Precise molecular imaging of GSCs by means of probes in vivo has therefore become a premise of solving the above problems. Herein, a sensitive, specific, accurate and biocompatible molecular nanoprobe is reported with MR/fluorescence imaging modalities for CD133+ glioma tumor bimodal targeted imaging. Cd-free high quality CuInS2/ZnS core/shell quantum dots (QDs) were synthesized for fluorescence imaging; DTPA-coupled BSA with Gd3+ chelation (BSA-DTPAGd) were prepared and used both for phase transfer of hydrophobic CuInS2/ZnS QDs and MR imaging modality. The resulting hydrophilic paramagnetic QDs (pQDs) were then linked with anti-CD133 monoclonal antibody, pQDs-CD133mAb denoting the framework of the entire molecular probe, for tumor targeting. The obtained pQDs-CD133mAb has a proper size (ca. 45 nm) and good colloidal stability. It exhibits a high quality fluorescent emission (ca. 630 nm) together with high longitudinal relaxivity (r1 = 15.2 mM−1 s−1) compared with that of commercial Magnevist (r1 = 3.12 mM−1 s−1). Dual modal imaging in vitro and in vivo shows potent tumor enhancement with administration of pQDs-CD133mAb. A biodistribution study indicates hepatobiliary and renal processing of pQDs-CD133mAb with no obvious toxicity. It could be therefore concluded, with a dual-modal imaging and targeting strategy, pQDs-CD133mAb presents a great potential as an alternative for accurate diagnosis of glioma.

Bimodal imaging has captured increasing interests due to its complementary characteristics of two kinds of imaging modalities. Among the various dual-modal imaging techniques, MR/fluorescence imaging has been widely studied owing to its high 3D resolution and sensitivity. There is, however, still a strong demand to construct biocompatible MR/fluorescence contrast agents with near-infrared (NIR) fluorescent emissions and high relaxivities. In this study, BSA-DTPAGd derived from bovine serum albumin (BSA) as a novel kind of biotemplate is employed for biomineralization of paramagnetic NIR Ag2S quantum dots (denoted as Ag2S@BSA-DTPAGd pQDs). This synthetic strategy is found to be bioinspired, environmentally benign, and straightforward. The obtained Ag2S@BSA-DTPAGd pQDs have fine sizes (ca. 6 nm) and good colloidal stability. They exhibit unabated NIR fluorescent emission (ca. 790 nm) as well as high longitudinal relaxivity (r1 = 12.6 mM–1 s–1) compared to that of commercial Magnevist (r1 = 3.13 mM–1 s–1). In vivo tumor-bearing MR and fluorescence imaging both demonstrate that Ag2S@BSA-DTPAGd pQDs have pronounced tiny tumor targeting capability. In vitro and in vivo toxicity study show Ag2S@BSA-DTPAGd pQDs are biocompatible. Also, biodistribution analysis indicates they can be cleared from body mainly via liver metabolism. This protein-mediated biomineralized Ag2S@BSA-DTPAGd pQDs presents great potential as a novel bimodal imaging contrast agent for tiny tumor diagnosis.

Photothermal therapy (PTT) is attracting increasing interest and becoming more widely used for skin cancer therapy in the clinic, as a result of its noninvasiveness and low systemic adverse effects. However, there is an urgent need to develop biocompatible PTT agents, which enable accurate imaging, monitoring, and diagnosis. Herein, a biocompatible Gd-integrated CuS nanotheranostic agent (Gd:CuS@BSA) was synthesized via a facile and environmentally friendly biomimetic strategy, using bovine serum albumin (BSA) as a biotemplate at physiological temperature. The as-prepared Gd:CuS@BSA nanoparticles (NPs) with ultrasmall sizes (ca. 9 nm) exhibited high photothermal conversion efficiency and good photostability under near-infrared (NIR) laser irradiation. With doped Gd species and strong tunable NIR absorbance, Gd:CuS@BSA NPs demonstrate prominent tumor-contrasted imaging performance both on the photoacoustic and magnetic resonance imaging modalities. The subsequent Gd:CuS@BSA-mediated PTT result shows high therapy efficacy as a result of their potent NIR absorption and high photothermal conversion efficiency. The immune response triggered by Gd:CuS@BSA-mediated PTT is preliminarily explored. In addition, toxicity studies in vitro and in vivo verify that Gd:CuS@BSA NPs qualify as biocompatible agents. A biodistribution study demonstrated that the NPs can undergo hepatic clearance from the body. This study highlights the practicality and versatility of albumin-mediated biomimetic mineralization of a nanotheranostic agent and also suggests that bioinspired Gd:CuS@BSA NPs possess promising imaging guidance and effective tumor ablation properties, with high spatial resolution and deep tissue penetration.Keywords: biomimetic mineralization; CuS; MR imaging; photoacoustic; photothermal therapy

Gd3+-ion-doped upconversion nanoparticles (UCNPs), integrating the advantages of upconversion luminescence and magnetic resonance imaging (MRI) modalities, are capturing increasing attention because they are promising to improve the accuracy of diagnosis. The embedded Gd3+ ions in UCNPs, however, have an indistinct MRI enhancement owing to the inefficient exchange of magnetic fields with the surrounding water protons. In this study, a novel approach is developed to improve the MR imaging sensitivity of Gd3+-ion-doped UCNPs. Bovine serum albumin (BSA) bundled with DTPA-Gd3+ (DTPAGd) is synthesized both as the MR imaging sensitivity synergist and phase-transfer ligand for the surface engineering of UCNPs. The external Gd3+ ion attachment strategy is found to significant improve the MR imaging sensitivity of Gd3+-ion-doped UCNPs. The relaxivity analysis shows that UCNPs@BSA·DTPAGd exhibit higher relaxivity values than do UCNPs@BSA without DTPAGd moieties. Another relaxivity study discloses a striking message that the relaxivity value does not always reflect the realistic MRI enhancement capability. The high concentration of Gd3+-ion-containing UCNPs with further surface-engineered BSA·DTPAGd (denoted as UCNPs–H@BSA·DTPAGd) exhibits a more pronounced MRI enhancement capability compared to the other two counterparts [UCNPs–N@BSA·DTPAGd and UCNPs–L@BSA·DTPAGd (−N and –L are denoted as zero and low concentrations of Gd3+ ion doping, respectively)], even though it holds the lowest r1 of 1.56 s–1 per mmol L–1 of Gd3+. The physicochemical properties of UCNPs are essentially maintained after BSA·DTPAGd surface decoration with good colloidal stability, in addition to improving the MR imaging sensitivity. In vivo T1-weighted MRI shows potent tumor-enhanced MRI with UCNPs–H@BSA·DTPAGd. An in vivo biodistribution study indicates that it is gradually excreted from the body via hepatobiliary and renal processing with no obvious toxicity. It could therefore be concluded, with improved MR imaging sensitivity by an internal and external incorporation of Gd3+ strategy, that UCNPs–H@BSA·DTPAGd presents great potential as an alternative in tumor-targeted MR imaging.

Dual-modal imaging techniques have gained intense attention for their potential role in the dawning era of tumor early accurate diagnosis. Chelate-free robust dual-modal imaging nanoprobes with high efficiency and low toxicity are of essential importance for tumor targeted dual-modal in vivo imaging. It is still a crucial issue to endow Cd-free dual-modal nanoprobes with bright fluorescence as well as high relaxivity. Herein, a facile synthetic strategy was developed to prepare Gd-doped CuInS/ZnS bimodal quantum dots (GCIS/ZnS, BQDs) with optimized properties. The fluorescent properties of the GCIS/ZnS BQDs can be thoroughly optimized by varying reaction temperature, aging time, and ZnS coating. The amount of Gd precursor can be well-controlled to realize the optimized balance between the MR relaxivity and optical properties. The obtained hydrophobic GCIS/ZnS BQDs were surface engineered into aqueous phase with PEGylated dextran-stearyl acid polymeric lipid vesicles (PEG-DS PLVs). Upon the phase transfer, the hydrophilic GCIS/ZnS@PLVs exhibited pronounced near-infrared fluorescence as well as high longitudinal relaxivity (r1 = 9.45 mM–1 S–1) in water with good colloidal stability. In vivo tumor-bearing animal experiments further verified GCIS/ZnS@PLVs could achieve tumor-targeted MR/fluorescence dual-modal imaging. No toxicity was observed in the in vivo and ex vivo experiments. The GCIS/ZnS@PLVs present great potential as bimodal imaging contrast agents for tumor diagnosis.Keywords: dual-modal imaging; fluorescence imaging; MRI; quantum dots; targeted imaging

•PEGylated SPIONs are synthesized via a one-pot facile route.•They show high relaxivity and low cytotoxicity.•Both liver and spleen are found significantly contrast-enhanced in MR scanning.•They can be cleared from the body via hepatobiliary processing over a period of 14 days.Polyethylene glycol (PEG)-coated superparamagnetic iron oxide nanoparticles (PEG·SPIONs) were prepared by a facile one-pot approach. The synthesized PEG·SPIONs were found to be uniform in size with an average hydrodynamic diameter of 11.7 nm. PEG·SPIONs exhibited excellent dispersibility in water, colloidal stability, and biocompatibility. The magnetic resonance imaging (MRI) properties of PEG·SPIONs were characterized both in vitro and in vivo. The dual contrast both in T1 and T2-weighted imaging was well enhanced with longitudinal and transverse relaxivity (r1, r2) of 35.92 s− 1 per mM of Fe3 + and 206.91 s− 1 per mM of Fe3 + respectively. In vivo T2-weighted MRI shows pronounced enhancement in the liver and spleen but not in T1-weighted MRI. Accumulations of nanoparticles were found primarily in the liver, spleen, and intestine, while much lower uptake in the kidney, heart, and lungs. A gradual excretion of PEG·SPIONs was observed via hepatobiliary (HB) processing over a period of 14 days. The toxicity of PEG·SPIONs was also evaluated in vitro and in vivo. PEG·SPIONs were found to be biocompatible by investigating organ tissues after hematoxylin–eosin staining. The conclusion of the study indicates a high potential of PEG·SPIONs in medical MRI.PEGylated superparamagnetic iron oxide nanoparticles are synthesized via a one-pot facile route. They show low cytotoxicity, and present good in vivo MRI enhancement.

Synthesis of CuInS-based quantum dots (QDs) in the organic phase is currently one of the fastest growing points of nanotechnology. Most of the reported CuInS-based QDs are hydrophobic and cannot be directly used for biomedical applications without phase transfer. We put forward a one-pot synthetic strategy aimed at fabricating hydrophilic Zn–Cu–In–S/ZnS (ZCIS/ZnS) quantum dots (QDs) to be used directly for in vivo imaging without surface treatment. This strategy is based on the use of a hydrophilic ligand (6-sulfanyl-1-hexanol, MPH) and non-coordinating solvents such as a low molecular weight polyethylene glycol (PEG, MW = 400 Da). The capping ligand MPH endows the obtained ZCIS/ZnS QDs with good hydrophilicity and therefore offers great opportunity for direct bioimaging applications without phase transfer. Experimental results have indicated that these so-called hydrophilic ZCIS/ZnS QDs show low cytotoxicity and are successfully utilized for in vivo imaging. Furthermore, the here reported strategy doesn't only present a synthetic idea, but also might stimulate other innovative ideas on fabricating hydrophilic or water-soluble ZCIS/ZnS QDs to be used directly for biological applications.

A unique biomineralization approach was developed to synthesize gadolinium-based hybrid (GH) nanoparticles for effective blood pool contrast agents. This approach is bioinspired, environmentally benign, and straightforward. As-prepared GH nanoparticles are biocompatible and well stable in serum. They exhibit much higher longitudinal relaxivity and transverse relaxivity in water (r1 and r2 values of 15.0 and 19.7 s−1 per mM of Gd3+, respectively) than those measured for Gd–DTPA solution (r1 and r2 values of 3.7 and 4.6 s−1 per mM of Gd3+, respectively). In vivo T1-weighted magnetic resonance imaging (MRI) in living mice shows that the GH nanoparticles have an intravascular half-life up to 1 h, much longer than that of Gd–DTPA (about 10 min). As the GH nanoparticles were found to be cleared gradually via hepatobiliary (HB) processing, they can also serve as ideal candidates for liver specific MR contrast agents. In particular, these GH nanoparticles are bioinspired and environmentally benign, therefore promising for medical imaging applications.

Nanoclusters of superparamagnetic iron oxide nanoparticles (SPION) are developed for liver-specific magnetic resonance imaging (MRI) by a unique synthesis route. The process is efficient, environmentally benign, and straight forward within five minutes. The clustering effect is triggered in the presence of bovine serum albumin (BSA) aqueous phase under ultrasonication condition. The hydrophobic SPION are densely self-assembled into BSA/SPION hybrid nanoclusters with a uniform size of ∼86 nm. The as-prepared BSA/SPION hybrid nanoclusters are found to be biocompatible and stable. They exhibit high transverse relaxivity and longitudinal relaxivity in water (r2 and r1 values are 600.8 and 4.3 s–1 per mM of Fe3+, respectively). In vivo T2-weighted MRI shows excellent enhancement in liver with an imaging time-window up to 48 h. In vivo biodistribution study indicates a gradual excretion of the nanoclusters via hepatobiliary (HB) processing. No toxicity is observed in the in vivo and ex vivo experiments. The BSA/SPION hybrid nanoclusters present great potential in MRI as the liver-specific contrast agents (CAs).Keywords: bovine serum albumin; iron oxide; liver; magnetic resonance imaging; ultrasound;

Multimodal imaging technique is an alternative approach to improve sensitivity of early cancer diagnosis. In this study, highly fluorescent and strong X-ray absorption coefficient gold nanoclusters (Au NCs) are synthesized as dual-modality imaging contrast agents (CAs) for fluorescent and X-ray dual-modality imaging. The experimental results show that the as-prepared Au NCs are well constructed with ultrasmall sizes, reliable fluorescent emission, high computed tomography (CT) value and fine biocompatibility. In vivo imaging results indicate that the obtained Au NCs are capable of fluorescent and X-ray enhanced imaging.Graphical abstractHighlights► Gold nanoclusters (Au NCs) are synthesized via ambient biomineralization approach. ► The synthesized Au NCs exhibit highly fluorescent and strong X-ray absorption coefficient. ► Au NCs as dual-modality imaging contrast agents (CAs) for fluorescent and X-ray dual-modality imaging.

Quantum dots (QDs) have been widely used as fluorescent probes in cell-targeted imaging. However, nonspecific binding to cellular membranes has been a major challenge. In this study, a new approach is developed for effective reduction of nonspecific binding by bovine serum albumin (BSA)-coated QDs in cell targeting. The experimental results show efficient transfer of hydrophobic QDs from organic to aqueous phase in the presence of BSA aqueous solution under ultrasonication. This ultrasonication-based approach is facile, rapid, and efficient. Stabilization of QDs is mainly achieved by multiple mercapto groups in BSA macromolecules as multidentate ligands and partially by hydrophobic interaction between BSA and pending fatty ligands on QDs. The water solubility of QDs is enhanced by the surface amino and carboxyl groups, which also provide reaction sites for conjugation of targeting ligands. The BSA-coated QDs, with an overwhelming majority of hydrodynamic diameter size of ca. 18 nm, are colloidally stable under both acidic and basic conditions and found to exhibit strong fluorescent intensities. The nonspecific cellular binding is effectively reduced by BSA-coated QDs, compared with the mercaptopropionic acid (MPA)-coated CdTe QDs. BSA-coated QDs are further functionalized with cyclic Arg-Gly-Asp (cRGD) peptide. The cell assays indicate their high target-selectivity in integrin αvβ3-expressed cell imaging.

Bifunctional nanoparticles with highly fluorescence and decent magnetic properties have been widely used in biomedical application. In this study, highly fluorescent magnetic nanoparticles (FMNPs) with uniform size of ca. 40 nm are prepared by encapsulation of both magnetic nanoparticles (MNPs) and shell/core quantum dots (QDs) with well-designed shell structure/compositions into silica matrix via a one-pot reverse microemulsion approach. The spectral analysis shows that the FMNPs hold high fluorescent quantum yield (QY). The QYs and saturation magnetization of the FMNPs can be regulated by varying the ratio of the encapsulated QDs to MNPs. Moreover, the surface of the FMNPs can be modified to offer chemical groups for antibody conjugation for following use in target-enrichment and subsequent fluorescent detection. The in vitro immunofluorescence assay and flow cytometric analysis indicate that the bifunctional FMNPs-antibody bioconjugates are capable of target-enrichment, magnetic separation and can also be used as alternative fluorescent probes on flow cytometry for biodetection.Graphical abstractHighly fluorescent magnetic nanoparticles were prepared based on the selection of proper type of quantum dots as the fluorescent moiety for the target-enrichment, magnetic separation and subsequent flow cytometric analysis.Research highlights► Highly fluorescent magnetic nanoparticles (FMNPs) are prepared by encapsulation of both MNPs and proper type of QDs into silica. ► FMNPs contained well-designed seven layered shell/core QDs hold high and stable QY. ► Both target-enrichment process and fluorescent detection step can be accomplished by the same single bifunctional FMNPs.

A unique biomineralization approach was developed to synthesize gadolinium-based hybrid (GH) nanoparticles for effective blood pool contrast agents. This approach is bioinspired, environmentally benign, and straightforward. As-prepared GH nanoparticles are biocompatible and well stable in serum. They exhibit much higher longitudinal relaxivity and transverse relaxivity in water (r1 and r2 values of 15.0 and 19.7 s−1 per mM of Gd3+, respectively) than those measured for Gd–DTPA solution (r1 and r2 values of 3.7 and 4.6 s−1 per mM of Gd3+, respectively). In vivo T1-weighted magnetic resonance imaging (MRI) in living mice shows that the GH nanoparticles have an intravascular half-life up to 1 h, much longer than that of Gd–DTPA (about 10 min). As the GH nanoparticles were found to be cleared gradually via hepatobiliary (HB) processing, they can also serve as ideal candidates for liver specific MR contrast agents. In particular, these GH nanoparticles are bioinspired and environmentally benign, therefore promising for medical imaging applications.

Currently, protein/peptide-based biomimetic mineralization has been demonstrated to be an efficient and promising strategy for synthesis of inorganic/metal nanoparticles (NPs) for bioapplications. This strategy is found to be bio-inspired, straightforward, and environmentally benign. It can produce inorganic/metal NPs with good stability, excellent biocompatibility, high water solubility, and rich surface functional groups for further bioconjunction. In this review, we provide a summary of the previously reported proteins/peptides as biotemplates involved in biomimetic mineralization synthesis, and categorize the obtained inorganic NPs ranging from metal nanoclusters (MNCs), quantum dots (QDs), gadolinium derivatives, and metal sulfide nanoparticles (MSNPs) with an emphasis on the recent progress in their use in biomedical applications, including bio-sensing, ion detection, bio-labeling, in vivo imaging and therapy. In the end, the challenges and future outlook in this emerging area are also discussed.

Glioma stem cells (GSCs) are considered the key to the occurrence, development, invasion, recurrence and sensitivity to treatment of brain tumors. Precise molecular imaging of GSCs by means of probes in vivo has therefore become a premise of solving the above problems. Herein, a sensitive, specific, accurate and biocompatible molecular nanoprobe is reported with MR/fluorescence imaging modalities for CD133+ glioma tumor bimodal targeted imaging. Cd-free high quality CuInS2/ZnS core/shell quantum dots (QDs) were synthesized for fluorescence imaging; DTPA-coupled BSA with Gd3+ chelation (BSA-DTPAGd) were prepared and used both for phase transfer of hydrophobic CuInS2/ZnS QDs and MR imaging modality. The resulting hydrophilic paramagnetic QDs (pQDs) were then linked with anti-CD133 monoclonal antibody, pQDs-CD133mAb denoting the framework of the entire molecular probe, for tumor targeting. The obtained pQDs-CD133mAb has a proper size (ca. 45 nm) and good colloidal stability. It exhibits a high quality fluorescent emission (ca. 630 nm) together with high longitudinal relaxivity (r1 = 15.2 mM−1 s−1) compared with that of commercial Magnevist (r1 = 3.12 mM−1 s−1). Dual modal imaging in vitro and in vivo shows potent tumor enhancement with administration of pQDs-CD133mAb. A biodistribution study indicates hepatobiliary and renal processing of pQDs-CD133mAb with no obvious toxicity. It could be therefore concluded, with a dual-modal imaging and targeting strategy, pQDs-CD133mAb presents a great potential as an alternative for accurate diagnosis of glioma.