Multidentate Polysarcosine-Based Ligands for Water-Soluble Quantum Dots

Concepts and Approaches to Reduce or Avoid Protein Corona Formation on Nanoparticles: Challenges and Opportunities

This review describes the formation of a protein corona (or its absence) on different classes of nanoparticles, its basic principles, and its consequences for nanomedicine. For this purpose, it describes general concepts to control (guide/minimize) the interaction between artificial nanoparticles and plasma proteins to reduce protein corona formation. Thereafter, methods for the qualitative or quantitative determination of protein corona formation are presented, as well as the properties of nanoparticle surfaces, which are relevant for protein corona prevention (or formation). Thereby especially the role of grafting density of hydrophilic polymers on the surface of the nanoparticle is discussed to prevent the formation of a protein corona. In this context also the potential of detergents (surfactants) for a temporary modification as well as grafting-to and grafting-from approaches for a permanent modification of the surface are discussed. The review concludes by highlighting several promising avenues. This includes (i) the use of nanoparticles without protein corona for active targeting, (ii) the use of synthetic nanoparticles without protein corona formation to address the immune system, (iii) the recollection of nanoparticles with a defined protein corona after in vivo application to sample the blood proteome and (iv) further concepts to reduce protein corona formation.

Polymer Brushes on Nanoparticles for Controlling the Interaction with Protein-Rich Physiological Media

The interaction of nanoparticles (NPs) with biological environments triggers the formation of a protein corona (PC), which significantly influences their behavior in vivo. This review explores the evolving understanding of PC formation, focusing on the opportunity for decreasing or suppressing protein-NP interactions by macromolecular engineering of NP shells. The functionalization of NPs with a dense, hydrated polymer brush shell is a powerful strategy for imparting stealth properties in order to elude recognition by the immune system. While poly(ethylene glycol) (PEG) has been extensively used for this purpose, concerns regarding its stability and immunogenicity have prompted the exploration of alternative polymers. The stealth properties of brush shells can be enhanced by tailoring functionalities and structural parameters, including the molar mass, grafting density, and polymer topology. Determining correlations between these parameters and biopassivity has enabled us to obtain polymer-grafted NPs with high colloidal stability and prolonged circulation time in biological media.

Recent progress on polySarcosine as an alternative to PEGylation: Synthesis and biomedical applications

Biotherapeutic PEGylation to prolong action of medications has gained popularity over the last decades. Various hydrophilic natural polymers have been developed to tackle the drawbacks of PEGylation, such as its accelerated blood clearance and non-biodegradability. Polypeptoides, such as polysarcosine (pSar), have been explored as hydrophilic substitutes for PEG. pSar has PEG-like physicochemical characteristics such as water solubility and no reported cytotoxicity and immunogenicity. This review discusses pSar derivatives, synthesis, characterization approaches, biomedical applications, in addition to the challenges and future perspectives of pSar based biomaterials as an alternative to PEG.

Introducing Savie: A Biodegradable Surfactant Enabling Chemo- and Biocatalysis and Related Reactions in Recyclable Water

Savie is a biodegradable surfactant derived from vitamin E and polysarcosine (PSar) developed for use in organic synthesis in recyclable water. This includes homogeneous catalysis (including examples employing only ppm levels of catalyst), heterogeneous catalysis, and biocatalytic transformations, including a multistep chemoenzymatic sequence. Use of Savie frequently leads to significantly higher yields than do conventional surfactants, while obviating the need for waste-generating organic solvents.

Fluorescent Nanoparticles for Super-Resolution Imaging

Super-resolution imaging techniques that overcome the diffraction limit of light have gained wide popularity for visualizing cellular structures with nanometric resolution. Following the pace of hardware developments, the availability of new fluorescent probes with superior properties is becoming ever more important. In this context, fluorescent nanoparticles (NPs) have attracted increasing attention as bright and photostable probes that address many shortcomings of traditional fluorescent probes. The use of NPs for super-resolution imaging is a recent development and this provides the focus for the current review. We give an overview of different super-resolution methods and discuss their demands on the properties of fluorescent NPs. We then review in detail the features, strengths, and weaknesses of each NP class to support these applications and provide examples from their utilization in various biological systems. Moreover, we provide an outlook on the future of the field and opportunities in material science for the development of probes for multiplexed subcellular imaging with nanometric resolution.

Designing the Surface Chemistry of Inorganic Nanocrystals for Cancer Imaging and Therapy

Inorganic nanocrystals, such as gold, iron oxide and semiconductor quantum dots, offer promising prospects for cancer diagnostics, imaging and therapy, due to their specific plasmonic, magnetic or fluorescent properties. The organic coating, or surface ligands, of these nanoparticles ensures their colloidal stability in complex biological fluids and enables their functionalization with targeting functions. It also controls the interactions of the nanoparticle with biomolecules in their environment. It therefore plays a crucial role in determining nanoparticle biodistribution and, ultimately, the imaging or therapeutic efficiency. This review summarizes the various strategies used to develop optimal surface chemistries for the in vivo preclinical and clinical application of inorganic nanocrystals. It discusses the current understanding of the influence of the nanoparticle surface chemistry on its colloidal stability, interaction with proteins, biodistribution and tumor uptake, and the requirements to develop an optimal surface chemistry.

Light-Mediated Synthesis and Reprocessing of Dynamic Bottlebrush Elastomers under Ambient Conditions

We introduce a novel grafting-through polymerization strategy to synthesize dynamic bottlebrush polymers and elastomers in one step using light to construct a disulfide-containing backbone. The key starting material-α-lipoic acid (LA)-is commercially available, inexpensive, and biocompatible. When installed on the chain end(s) of poly(dimethylsiloxane) (PDMS), the cyclic disulfide unit derived from LA polymerizes under ultraviolet (UV) light in ambient conditions. Significantly, no additives such as initiator, solvent, or catalyst are required for efficient gelation. Formulations that include bis-LA-functionalized cross-linker yield bottlebrush elastomers with high gel fractions (83-98%) and tunable, supersoft shear moduli in the ∼20-200 kPa range. An added advantage of these materials is the dynamic disulfide bonds along each bottlebrush backbone, which allow for light-mediated self-healing and on-demand chemical degradation. These results highlight the potential of simple and scalable synthetic routes to generate unique bottlebrush polymers and elastomers based on PDMS.

Bioorthogonal hydroxyethyl cellulose-based scaffold crosslinked via click chemistry for cartilage tissue engineering applications

In this study, azide and alkyne moieties were introduced to the structure of citric acid-modified hydroxyethyl cellulose (HEC) and then through a bioorthogonal click chemistry method: Strain-promoted azide-alkyne cycloaddition, a novel crosslinked HEC scaffold (click sample) was obtained. Chemical modifications and successful crosslinking of the samples were assessed with FTIR and ¹H NMR spectroscopy. Lyophilized samples exhibited a porous interconnected microarchitecture with desirable features for commensurate cartilage tissue engineering applications. As the stability of scaffolds improved upon crosslinking, considerable water uptake and swelling degree of ~650% could still be measured for the click sample. Offering Young's modulus of ~10 MPa and tensile strength of ~0.43 MPa, the mechanical characteristics of click sample were comparable with those of normal cartilage tissue. Various in vitro biological assays, including MTT analysis, cellular attachment, histological staining with safranin O, and real-time PCR decisively approved significant biocompatibility, chondrogenic ability, and bioorthogonal features of click sample.

Ugi Reaction of Amino Acids: From Facile Synthesis of Polypeptoids to Sequence-Defined Macromolecules

Polypeptoids have been prepared and researched for more than 20 years. However, the efficient generation of polypeptoids and sequence-defined polypeptoids faces many challenges and difficulties. The Ugi reaction of amino acids has recently been introduced into polypeptoid chemistry as a new and powerful method to furnish polypeptoids. In the following mini review, the recent progress on the application of the Ugi reaction of amino acids in polypeptoid science, including polypeptoid from sustainable furfural, sequence-defined polypeptoids, and more is summarized. Moreover, the future development of the Ugi reaction of amino acids in polypeptoid science is discussed.

Functionalizing nanoparticles with cancer-targeting antibodies: A comparison of strategies

Standard cancer therapies sometimes fail to deliver chemotherapeutic drugs to tumor cells in a safe and effective manner. Nanotechnology takes the lead in providing new therapeutic options for cancer due to major potential for selective targeting and controlled drug release. Antibodies and antibody fragments are attracting much attention as a source of targeting ligands to bind specific receptors that are overexpressed on cancer cells. Therefore, researchers are devoting time and effort to develop targeting strategies based on nanoparticles functionalized with antibodies, which hold great promise to enhance therapeutic efficacy and circumvent severe side effects. Several methods have been described to immobilize antibodies on the surface of nanoparticles. However, selecting the most appropriate for each application is challenging but also imperative to preserve antigen binding ability and yield stable antibody-conjugated nanoparticles. From this perspective, we aim to provide considerable knowledge on the most widely used methods of functionalization that can be helpful for decision-making and design of conjugation protocols as well. This review summarizes adsorption, covalent conjugation (carbodiimide, maleimide and "click" chemistries) and biotin-avidin interaction, while discussing the advantages, limitations and relevant therapeutic approaches currently under investigation.

Subnanomolar FRET-Based DNA Assay Using Thermally Stable Phosphorothioated DNA-Functionalized Quantum Dots

Quantum dots (QDs) can serve as an attractive Förster resonance energy transfer (FRET) donor for DNA assay due to their excellent optical properties. However, the specificity and sensitivity of QD-based FRET analysis are prominently reduced by nonspecific DNA adsorption and poor colloidal stability during DNA hybridization, which hinders the practical applications of QDs as a biosensing platform. Here, we report subnanomolar FRET assay of DNA through the stabilization of DNA/QD interface using DNA-functionalized QDs with phosphorothioated single-stranded DNA (pt-ssDNA) as a multivalent ligand in an aqueous solution. In situ DNA functionalization was achieved during the aqueous synthesis of CdTe/CdS QDs, resulting in the maximum photoluminescence quantum yields of 76.9% at an emission wavelength of 732 nm. Conventional monothiolated ssDNA-capped QDs exhibited particle aggregation and photoluminescence (PL) quenching during DNA hybridization at 70 °C due to the dissociation of surface ligands. Such colloidal instability induced the nonspecific adsorption of DNA, resulting in false-positive signal and decreased sensitivity with the limit of detection (LOD) of 16.1 nM. In contrast, the pt-ssDNA-functionalized QDs maintained their colloidal stability and PL properties at elevated temperatures. The LOD of the pt-ssDNA-functionalized QDs was >30 times lower (0.47 nM) while maintaining the high specificity to a target sequence because the strong multivalent binding of pt-ssDNA to the surface of QDs prevents the detachment of pt-ssDNA and nonspecific adsorption of DNA. The study suggests that the ligand design to stabilize the surface of QDs in an aqueous milieu is critically important for the high performance of QDs for specific DNA assay.

Recent advances in colloidal nanocomposite designviaheterogeneous polymerization techniques

Recent advances in colloidal nanocomposite design by heterogeneous polymerization are reviewed, with a specific focus on encapsulation and particle-based stabilization for specific materials applications.

Efficient Shielding of Polyplexes Using Heterotelechelic Polysarcosines

Shielding agents are commonly used to shield polyelectrolyte complexes, e.g., polyplexes, from agglomeration and precipitation in complex media like blood, and thus enhance their in vivo circulation times. Since up to now primarily poly(ethylene glycol) (PEG) has been investigated to shield non-viral carriers for systemic delivery, we report on the use of polysarcosine (pSar) as a potential alternative for steric stabilization. A redox-sensitive, cationizable lipo-oligomer structure (containing two cholanic acids attached via a bioreducible disulfide linker to an oligoaminoamide backbone in T-shape configuration) was equipped with azide-functionality by solid phase supported synthesis. After mixing with small interfering RNA (siRNA), lipopolyplexes formed spontaneously and were further surface-functionalized with polysarcosines. Polysarcosine was synthesized by living controlled ring-opening polymerization using an azide-reactive dibenzo-aza-cyclooctyne-amine as an initiator. The shielding ability of the resulting formulations was investigated with biophysical assays and by near-infrared fluorescence bioimaging in mice. The modification of ~100 nm lipopolyplexes was only slightly increased upon functionalization. Cellular uptake into cells was strongly reduced by the pSar shielding. Moreover, polysarcosine-shielded polyplexes showed enhanced blood circulation times in bioimaging studies compared to unshielded polyplexes and similar to PEG-shielded polyplexes. Therefore, polysarcosine is a promising alternative for the shielding of non-viral, lipo-cationic polyplexes.

Synthesis and Properties of Alternating Polypeptoids and Polyampholytes as Protein-Resistant Polymers

Alternating polypeptoids are particularly appealing because alternating sequence may impart highly ordered structure and special functions, while their simple synthesis still remains a key challenge. We describe that natural amino acid monomers can be polymerized via Ugi reaction in a step-growth fashion as an AA' BB' system, which leads to alternating polypeptoids with molecular weight up to 15 kg/mol. These alternating polypeptoids are thermally responsive and exhibit cloud points ( T_cp) between 27 and 37 °C. Importantly, the marriage of high functionality of amino acids with Ugi reaction also enables the preparation of polypeptoids encoding both protected amino and carboxyl groups in the side chains with alternating arrangement. The cleavage of the protecting groups leads to alternating polyampholytes without any compositional drift. Such alternating polyampholytes not only exhibit high water solubility (>100 mg/mL) but also demonstrate the ability to resist aggregation with proteins. Moreover, the cell viability measurements reveal that these materials have minimal cytotoxicity to HeLa cells. Overall, this study offers us a simple way to prepare a variety of polypeptoids and polyampholytes as new protein-resistant materials for bioapplications.

Beyond PEGylation: Alternative surface-modification of nanoparticles with mucus-inert biomaterials

Mucus is a highly hydrated viscoelastic gel present on various moist surfaces in our body including the eyes, nasal cavity, mouth, gastrointestinal, respiratory and reproductive tracts. It serves as a very efficient barrier that prevents harmful particles, viruses and bacteria from entering the human body. However, the protective function of the mucus also hampers the diffusion of drugs and nanomedicines, which dramatically reduces their efficiency. Functionalisation of nanoparticles with low molecular weight poly(ethylene glycol) (PEGylation) is one of the strategies to enhance their penetration through mucus. Recently a number of other polymers were explored as alternatives to PEGylation. These alternatives include poly(2-alkyl-2-oxazolines), polysarcosine, poly(vinyl alcohol), other hydroxyl-containing non-ionic water-soluble polymers, zwitterionic polymers (polybetaines) and mucolytic enzymes. This review discusses the studies reporting the use of these polymers or potential application to facilitate mucus permeation of nanoparticles.

Polysarcosine brush stabilized gold nanorods for in vivo near-infrared photothermal tumor therapy

Gold nanorods (AuNRs) are suitable candidates for photothermal therapy in vivo, because of their excellent ability to transfer near-infrared (NIR) light into heat. However, appropriate surface should be generated on AuNRs before their in vivo application because of the low colloidal stability in complicate biological environment and relatively strong toxicity compared to their pristine stabilizer cetyltrimethylammonium bromide. In the current study, polysarcosine (PS), a non-ionic hydrophilic polypeptoid whose structure is similar to polypeptides, bearing repeating units of natural α-amino acid, was used to stabilize AuNRs due to its excellent hydrophilicity and biocompatibility. Polysarcosine with optimized molecular weight was synthesized and used to modify AuNRs by traditional ligand exchange. The grafting of PS on AuNRs was evidenced by fourier transform infrared (FTIR) spectroscopy and the alternation of surface zeta potential. The polysarcosine coated AuNRs (Au@PS) showed good stabilities in wide pH range and simulated physiological buffer with the ligand competition of dithiothreitol (DTT). The Au@PS NRs had neglectable cytotoxicity and showed efficient ablation of tumor cells in vitro. Moreover, Au@PS NRs had a longer circulation time in body that resulted in a higher accumulation in solid tumors after intravenous injection, compared to AuNRs capped with polyethylene glycol (PEG). Photothermal therapy in vivo demonstrated that the tumors were completely destroyed by single-time irradiation of NIR laser after one-time injection of the polysarcosine capped AuNRs. The Au@PS NRs did not cause obvious toxicity in vivo, suggesting promising potential in cancer therapy.

STATEMENT OF SIGNIFICANCE

In current study, polysarcosine (PS), a non-ionic hydrophilic polypeptoid whose structure is similar to polypeptides, bearing repeating units of natural α-amino acid, was used to stabilize AuNRs due to its excellent hydrophilicity and biocompatibility. The polysarcosine coated AuNRs (Au@PS) showed good stabilities in wide pH range and simulated physiological buffer. The Au@PS NRs had very low cytotoxicity and showed high efficacy for the ablation of cancer cells in vitro. Moreover, Au@PS NRs had a longer circulation time in blood that led to a higher accumulation in tumors after intravenous injection, compared to AuNRs capped with polyethylene glycol (PEG). In vivo photothermal therapy showed that tumors were completely cured without reoccurrence by one-time irradiation of NIR laser after a single injection of the polysarcosine modified AuNRs.

Amphiphilic star-shaped poly(sarcosine)-block-poly(ε-caprolactone) diblock copolymers: one-pot synthesis, characterization, and solution properties

We firstly synthesized amphiphilic three-armed star-shaped poly(sarcosine)-block-poly(ε-caprolactone) diblock copolymers (s-PSar-b-PCLs), and investigated the solution properties and biocompatibility of the copolymers.

Application of semiconductor quantum dots in bioimaging and biosensing

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing.

Organic-to-aqueous phase transfer of Zn–Cu–In–Se/ZnS quantum dots with multifunctional multidentate polymer ligands for biomedical optical imaging

ZnCuInSe/ZnS QDs with widely tunable PL emissions were synthesized and water-solubilized with cRGD modified multifunctional multidentate polymer (cRGD-PME) for bioimaging.

Orthogonally reactive amino acids and end groups in NCA polymerization

We summarize recent strategies for the synthesis of orthogonally reactive polypeptides and polypeptoids by direct and post-polymerization approaches.

Suppressing the Fluorescence Blinking of Single Quantum Dots Encased in N-type Semiconductor Nanoparticles

N-type semiconductor indium tin oxide (ITO) nanoparticles are used to effectively suppress the fluorescence blinking of single near-infrared-emitting CdSeTe/ZnS core/shell quantum dots (QDs), where the ITO could block the electron transfer from excited QDs to trap states and facilitate more rapid regeneration of neutral QDs by back electron transfer. The average blinking rate of QDs is significantly reduced by more than an order of magnitude and the largest proportion of on-state is 98%, while the lifetime is not considerably reduced. Furthermore, an external electron transfer model is proposed to analyze the possible effect of radiative, nonradiative, and electron transfer pathways on fluorescence blinking. Theoretical analysis based on the model combined with measured results gives a quantitative insight into the blinking mechanism.

Polymer-inorganic hybrid nanoparticles of various morphologies via polymerization-induced self assembly and sol–gel chemistry

The preparation of polymer-silica hybrid nanoparticles of various morphologies is reported.