Clickable-Zwitterionic Copolymer Capped-Quantum Dots for in Vivo Fluorescence Tumor Imaging

Recent advances of multifunctional zwitterionic polymers for biomedical application

Zwitterionic polymers possess equal total positive and negative charges in the repeating units, making them electrically neutral overall. This unique property results in superhydrophilicity, which makes the zwitterionic polymers highly effective in resisting protein adsorption, thus endowing the drug carriers with long blood circulation time, inhibiting thrombus formation on biomedical devices in contact with blood, and ensuring the good sensitivity of sensors in biomedical application. Moreover, zwitterionic polymers have tumor-targeting ability and pH-responsiveness, rendering them ideal candidates for antitumor drug delivery. Additionally, the high ionic conductivity of zwitterionic polymers makes them an important raw material for ionic skin. Zwitterionic polymers exhibit remarkable resistance to bacterial adsorption and growth, proving their suitability in a wide range of biomedical applications such as ophthalmic applications, and wound dressings. In this paper, we provide an in-depth analysis of the different structures and characteristics of zwitterionic polymers and highlight their unique qualities and suitability for biomedical applications. Furthermore, we discuss the limitations and challenges that must be overcome to realize the full potential of zwitterionic polymers and present an optimistic perspective for zwitterionic polymers in the biomedical fields. STATEMENT OF SIGNIFICANCE: Zwitterionic polymers have a series of excellent properties such as super hydrophilicity, anti-protein adsorption, antibacterial ability and good ionic conductivity. However, biomedical applications of multifunctional zwitterionic polymers are still a major field to be explored. This review focuses on the design and application of zwitterionic polymers-based nanosystems for targeted and responsive delivery of antitumor drugs and cancer diagnostic agents. Moreover, the use of zwitterionic polymers in various biomedical applications such as biomedical devices in contact with blood, biosensors, ionic skin, ophthalmic applications and wound dressings is comprehensively described. We discuss current results and future challenges for a better understanding of multifunctional zwitterionic polymers for biomedical applications.

Affinity Capillary Electrophoresis as a Tool To Characterize Molecularly Imprinted Nanogels in Solution

In this work, an innovative and accurate affinity capillary electrophoresis (ACE) method was set up to monitor the complexation of aqueous MIP nanogels (NGs) with model cancer-related antigens. Using α2,6'- and α2,3'-sialyllactose as oversimplified cancer biomarker-mimicking templates, NGs were synthesized and characterized in terms of size, polydispersity, and overall charge. A stability study was also carried out in order to select the best storage conditions and to ensure product quality. After optimization of capillary electrophoresis conditions, injection of MIP NGs resulted in a single, sharp, and efficient peak. The mobility shift approach was applied to quantitatively estimate binding affinity, in this case resulting in an association constant of K ≈ 106 M-1. The optimized polymers further displayed a pronounced discrimination between the two sialylated sugars. The newly developed ACE protocol has the potential to become a very effective method for nonconstrained affinity screening of NG in solution, especially during the NG development phase and/or for a final accurate quantitation of the observed binding.

Sulfobetaine-Phosphonate Block Copolymer Coated Iron Oxide Nanoparticles for Genomic Locus Targeting and Magnetic Micromanipulation in the Nucleus of Living Cells

Exerting forces on biomolecules inside living cells would allow us to probe their dynamic interactions in their native environment. Magnetic iron oxide nanoparticles represent a unique tool capable of pulling on biomolecules with the application of an external magnetic field gradient; however, their use has been restricted to biomolecules accessible from the extracellular medium. Targeting intracellular biomolecules represents an additional challenge due to potential nonspecific interactions with cytoplasmic or nuclear components. We present the synthesis of sulfobetaine-phosphonate block copolymer ligands, which provide magnetic nanoparticles that are stealthy and targetable in living cells. We demonstrate, for the first time, their efficient targeting in the nucleus and their use for magnetic micromanipulation of a specific genomic locus in living cells. We believe that these stable and sensitive magnetic nanoprobes represent a promising tool to manipulate specific biomolecules in living cells and probe the mechanical properties of living matter at the molecular scale.

Zwitterionic Polymers toward the Development of Orientation-Sensitive Bioprobes

Dynamics with an orientational degree of freedom are fundamental in biological events. Probes with polarized luminescence enable a determination of the orientation. Lanthanide-doped nanocrystals can provide more precise analysis than quantum dots due to the nonphotoblinking/bleaching nature and the multiple line-shaped emission. However, the intrinsic polarization property of the original nanocrystals often deteriorates in complex physiological environments because the colloidal stability easily breaks and the probes aggregate in the media with abundant salts and macromolecules. Engineering the surface chemistry of the probes is thus essential to be compatible with biosystems, which has remained a challenging task that should be exclusively addressed for each specific probe. Here, we demonstrate a facile and efficient surface functionalization of lanthanide-doped nanorods by zwitterionic block copolymers. Due to the steric interaction and the intrinsic zwitterionic nature of the polymers, high colloidal stability of the zwitterionic nanorod suspension is achieved over wide ranges of pH and concentration of salts, even giving rise to the lyotropic liquid crystalline behavior of the nanorods in physiological media. The shear-aligned ability is shown to be unaltered by the coated polymers, and thus, the strongly polarized emission of Eu³⁺ is preserved. Besides, biological experiments reveal good biocompatibility of the zwitterionic nanorods with negligible nonspecific binding. This study is a stepping stone for the use of the nanorods as orientation probes in biofluids and validates the strategy of coupling zwitterions to lanthanide-doped nanocrystals for various bioapplications.

Spectral analysis on the acceptor concentration-dependent fluorescence resonance energy transfer process in CuInS2@ZnS-SQ complexes

Owing to the broad spectral response and flexible choices of donors and acceptors, fluorescence resonance energy transfer (FRET) system based on quantum dots (QDs) is a potential candidate for enhancing performance of solar cells and other optoelectronic devices. Thus it is necessary to develop such FRET systems with high efficiency and understand the involved photophysical dynamics. Here, with type I CuInS₂@ZnS core-shell quantum dots as the energy donor, series of CuInS₂@ZnS-SQ complexes are synthesized by adjusting the acceptor (squaric acid, SQ) concentration. The FRET dynamics of the samples is systematically investigated by virtue of steady-state emission, time-resolved fluorescence decay, and transient absorption measurements. The experimental results display a positive correlation between the energy transfer efficient (η). The best energy transfer efficient achieved from experimental data is 52%. This work provides better understanding of the photophysical dynamics in similar complexes and facilitates further development of new photoelectronic devices based on relevant FRET systems.

Synthesis of bio-templated clickable quantum dots and dual-emitting organic/inorganic complex for ratiometric fluorescence visual assay of blood glucose

With the prevalence of diabetes, rapid and simple blood glucose monitoring becomes more and more important. Here, we reported the synthesis of the bio-templated N3-CdZnTeS quantum dots (QDs), which was...

Thermodynamics of nanocrystal–ligand binding through isothermal titration calorimetry

Manipulations of nanocrystal (NC) surfaces have propelled the applications of colloidal NCs across various fields such as bioimaging, catalysis, electronics, and sensing applications.

Advanced Nanomaterials-Assisted Cell Cryopreservation: A Mini Review

Cell cryopreservation is of vital significance both for transporting and storing cells before experimental/clinical use. Cryoprotectants (CPAs) are necessary additives in the preserving medium in cryopreservation, preventing cells from freeze-thaw injuries. Traditional organic solvents have been widely used in cell cryopreservation for decades. Given the obvious damage to cells due to their undesirable cytotoxicity and the burdensome post-thaw washing cycles before use, traditional CPAs are more and more likely to be replaced by modern ones with lower toxicity, less processing, and higher efficiency. As materials science thrives, nanomaterials are emerging to serve as potent vehicles for delivering nontoxic CPAs or inherent CPAs comparable to or even superior to conventional ones. This review will introduce some advanced nanomaterials (e.g., organic/inorganic nanoCPAs, nanodelivery systems) utilized for cell cryopreservation, providing broader insights into this developing field.

Quantum Dots for Improved Single-Molecule Localization Microscopy

Colloidal semiconductor quantum dots (QDs) have long established their versatility and utility for the visualization of biological interactions. On the single-particle level, QDs have demonstrated superior photophysical properties compared to organic dye molecules or fluorescent proteins, but it remains an open question as to which of these fundamental characteristics are most significant with respect to the performance of QDs for imaging beyond the diffraction limit. Here, we demonstrate significant enhancement in achievable localization precision in QD-labeled neurons compared to neurons labeled with an organic fluorophore. Additionally, we identify key photophysical parameters of QDs responsible for this enhancement and compare these parameters to reported values for commonly used fluorophores for super-resolution imaging.

NIR Imaging of the Integrin-Rich Head and Neck Squamous Cell Carcinoma Using Ternary Copper Indium Selenide/Zinc Sulfide-Based Quantum Dots

The efficient intraoperative identification of cancers requires the development of the bright, minimally-toxic, tumor-specific near-infrared (NIR) probes as contrast agents. Luminescent semiconductor quantum dots (QDs) offer several unique advantages for in vivo cellular imaging by providing bright and photostable fluorescent probes. Here, we present the synthesis of ZnCuInSe/ZnS core/shell QDs emitting in NIR (~750 nm) conjugated to NAVPNLRGDLQVLAQKVART (A20FMDV2) peptide for targeting α_vβ₆ integrin-rich head and neck squamous cell carcinoma (HNSCC). Integrin α_vβ₆ is usually not detectable in nonpathological tissues, but is highly upregulated in HNSCC. QD-A20 showed α_vβ₆ integrin-specific binding in two-dimension (2D) monolayer and three-dimension (3D) spheroid in vitro HNSCC models. QD-A20 exhibit limited penetration (ca. 50 µm) in stroma-rich 3D spheroids. Finally, we demonstrated the potential of these QDs by time-gated fluorescence imaging of stroma-rich 3D spheroids placed onto mm-thick tissue slices to mimic imaging conditions in tissues. Overall, QD-A20 could be considered as highly promising nanoprobes for NIR bioimaging and imaging-guided surgery.

Superior Properties and Biomedical Applications of Microorganism-Derived Fluorescent Quantum Dots

Quantum dots (QDs) are fluorescent nanocrystals with superb photo-physical properties. Applications of QDs have been exponentially increased during the past decade. They can be employed in several disciplines, including biological, optical, biomedical, engineering, and energy applications. This review highlights the structural composition and distinctive features of QDs, such as resistance to photo-bleaching, wide range of excitations, and size-dependent light emission features. Physical and chemical preparation of QDs have prominent downsides, including high costs, regeneration of hazardous byproducts, and use of external noxious chemicals for capping and stabilization purposes. To eliminate the demerits of these methods, an emphasis on the latest progress of microbial synthesis of QDs by bacteria, yeast, and fungi is introduced. Some of the biomedical applications of QDs are overviewed as well, such as tumor and microRNA detection, drug delivery, photodynamic therapy, and microbial labeling. Challenges facing the microbial fabrication of QDs are discussed with the future prospects to fully maximize the yield of QDs by elucidating the key enzymes intermediating the nucleation and growth of QDs. Exploration of the distribution and mode of action of QDs is required to promote their biomedical applications.

Three-dimensional flower-like shaped Bi5O7I particles incorporation zwitterionic fluorinated polymers with synergistic hydration-photocatalytic for enhanced marine antifouling performance

Herein, several novel composite films consisting of three-dimensional (3D) Bi₅O₇I flower-like shaped microsphere and zwitterionic fluorinated polymer (ZFP) were successfully fabricated with the aim of achieving high anti-fouling performance. The prepared Bi₅O₇I flower-like shaped microsphere particles with diameters in the range of 2∼3 μm were uniformly distributed on the surface and in the internal of ZFP. Benefiting from the hydration layer formed by the ZFP and the efficient photocatalytic performance of Bi₅O₇I flower-like microsphere, the resultant optimized Bi₅O₇I/ZFP composite film exhibited an excellent diatom anti-settling performance and a high antibacterial rate of 99.09% and 99.66% towards Escherichia coli and Staphylococcus aureus. In addition, the composite films possessed the strengthened visible light absorption, the effectively separation and transfer of the photo-induced electrons and holes, the large number of hydroxyl (OH) radicals and superoxide radicals (O₂^-) all in Bi₅O₇I/ZFP systems, all of which were beneficial for the photocatalytic antifouling activity. More importantly, the synergistic hydration-photocatalytic effect of the Bi₅O₇I/ZFP composite films are answerable for the improvement of the antifouling property compared to the control. Thus, the synergistic hydration-photocatalytic contribution of Bi₅O₇I/ZFP composite film will shows promise for potential application in marine antifouling.

Zwitterion and Oligo(ethylene glycol) Synergy Minimizes Nonspecific Binding of Compact Quantum Dots

Quantum dots (QDs) are a class of fluorescent nanocrystals in development as labels for molecular imaging in cells and tissues. Recently, coatings for quantum dots based on multidentate polymers have improved labeling performance in a range of bioanalytical applications, primarily due to reduced probe hydrodynamic size. Now, an ongoing challenge is to eliminate nonspecific binding between these small probes and cellular components that mask specifically labeled molecules. Here, we describe insights into controlling and minimizing intermolecular interactions governing nonspecific binding using multidentate polymers with tunable hydrophilic functional groups that are cationic, anionic, zwitterionic (ZW), or nonionic (oligoethylene glycol; OEG). By fixing surface-binding groups and polymer length, coated colloids have similar sizes but diverse physicochemical properties. We measure binding to globular proteins, fixed cells, and living cells and observe a substantial improvement in nonspecific binding resistance when surfaces are functionalized with a combination of ZW and OEG. The independent underlying effects of counterion adsorption and flexibility appear to synergistically resist adsorption when combined, particularly for fixed cells enriched in both charged and hydrophobic moieties. We further show that ZW-OEG QDs are stable under diverse conditions and can be self-assembled with antibodies to specifically label surface antigens on living cells and cytoplasmic proteins in fixed cells. This surface engineering strategy can be adopted across the diverse range of colloidal materials currently in use and in development for biomedical applications to optimize their molecular labeling specificity.

Shell-Free Copper Indium Sulfide Quantum Dots Induce Toxicity in Vitro and in Vivo

Semiconductor quantum dots (QDs) are attractive fluorescent contrast agents for in vivo imaging due to their superior photophysical properties, but traditional QDs comprise toxic materials such as cadmium or lead. Copper indium sulfide (CuInS₂, CIS) QDs have been posited as a nontoxic and potentially clinically translatable alternative; however, previous in vivo studies utilized particles with a passivating zinc sulfide (ZnS) shell, limiting direct evidence of the biocompatibility of the underlying CIS. For the first time, we assess the biodistribution and toxicity of unshelled CIS and partially zinc-alloyed CISZ QDs in a murine model. We show that bare CIS QDs breakdown quickly, inducing significant toxicity as seen in organ weight, blood chemistry, and histology. CISZ demonstrates significant, but lower, toxicity compared to bare CIS, while our measurements of core/shell CIS/ZnS are consistent with literature reports of general biocompatibility. In vitro cytotoxicity is dose-dependent on the amount of metal released due to particle degradation, linking degradation to toxicity. These results challenge the assumption that removing heavy metals necessarily reduces toxicity: indeed, we find comparable in vitro cytotoxicity between CIS and CdSe QDs, while CIS caused severe toxicity in vivo compared to CdSe. In addition to highlighting the complexity of nanotoxicity and the differences between the in vitro and in vivo outcomes, these unexpected results serve as a reminder of the importance of assessing the biocompatibility of core QDs absent the protective ZnS shell when making specific claims of compositional biocompatibility.

Antifouling and pH-Responsive Poly(Carboxybetaine)-Based Nanoparticles for Tumor Cell Targeting

Nanocarriers with responsibility and surface functionality of targeting molecules have been widely used to improve therapeutic efficiency. Hence, we report the assembly of pH-responsive and targeted polymer nanoparticles (NPs) composed of poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) as the core and poly(carboxybetaine methacrylate) (PCBMA) as the shell, functionalized with cyclic peptides containing Arginine-Glycine-Aspartic acid-D-Phenylalanine-Lysine (RGD). The resulting polymer NPs (PDPA@PCBMA-RGD NPs) can maintain the pH-responsivity of PDPA (pKa ~6.5) and low-fouling property of PCBMA that significantly resist non-specific interactions with RAW 264.7 and HeLa cells. Meanwhile, PDPA@PCBMA-RGD NPs could specifically target αvβ3 integrin-expressed human glioblastoma (U87) cells. The pH-responsiveness and low-fouling properties of PDPA@PCBMA NPs are comparable to PDPA@poly(ethylene glycol) (PDPA@PEG) NPs, which indicates that PCBMA is an alternative to PEG for low-fouling coatings. The advantage of PDPA@PCBMA NPs lies in the presence of carboxyl groups on their surfaces for further modification (e.g., RGD functionalization for cell targeting). The reported polymer NPs represent a new carrier that have the potential for targeted therapeutic delivery.

A versatile and accessible polymer coating for functionalizable zwitterionic quantum dots with high DNA grafting efficiency

Efficient and versatile functionalization of poly(anhydride maleic-alt-isobutylene) (PIMA), with economical commercial reagents, results in the one-step/one-day production of a copper-free click chemistry-ready carboxybetaine-like coating for quantum dots (QDs). The QDs are bright and stable in aqueous media and easily grafted with DNA with >95% efficiency.

Quantum dots from microfluidics for nanomedical application

Nanomedicine, with its advantages of rapid diagnosis, high sensitivity and high accuracy, has aroused extensive interest of researchers, as the cornerstone of nanomedicine, nanomaterials achieve extra attention and rapid development. Among nanomaterials, quantum dots stand out due to their long fluorescence lifetime and excellent antiphotobleaching performance. At present, quantum dots have been applied to the diagnosis and treatment of diseases and various strategies have been presented to fabricate quantum dots. Microfluidic is one promising strategy since microfluidic device can provide an effective platform for the diagnosis of trace disease markers. In this paper, research progress in the microfluidic synthesis of quantum dots and quantum dot-based nanomedical application is discussed. The classification of quantum dots is firstly introduced, and the researches on quantum dots synthesis based on microfluidic is then mainly described, including the sort, design, preparation of microfluidic synthesis device and its application in synthesis. Nanomedical applications of the quantum dots is especially described and emphasized. The prospects for future development of quantum dots from microfluidic for nanomedical application are finally presented. This article is categorized under: Diagnostic Tools > in vitro Nanoparticle-Based Sensing.

Imaging of Red-Shifted Light From Bioluminescent Tumors Using Fluorescence by Unbound Excitation From Luminescence

Early detection of tumors is today a major challenge and requires sensitive imaging methodologies coupled with new efficient probes. In vivo optical bioluminescence imaging has been widely used in the field of preclinical oncology to visualize tumors and several cancer cell lines have been genetically modified to provide bioluminescence signals. However, the light emitted by the majority of commonly used luciferases is usually in the blue part of the visible spectrum, where tissue absorption is still very high, making deep tissue imaging non-optimal, and calling for optimized optical imaging methodologies. We have previously shown that red-shifting of bioluminescence signal by Fluorescence Unbound Excitation from Luminescence (FUEL) is a mean to increase bioluminescence signal sensitivity detection in vivo. Here, we applied FUEL to tumor detection in two different subcutaneous tumor models: the auto-luminescent human embryonic kidney (HEK293) cell line and the murine B16-F10 melanoma cell line previously transfected with a plasmid encoding the Luc2 firefly luciferase. Tumor size and bioluminescence were measured over time and tumor vascularization characterized. We then locally injected near infrared emitting Quantum Dots (NIR QDs) in the tumor site and observed a red-shifting of bioluminescence signal by (FUEL) indicating that FUEL could be used to allow deeper tumor detection in mice.

Photostability of quantum dot micelles under ultraviolet irradiation

Phospholipid quantum dot micelles are useful for bio-applications because of their amphiphilicity and exceptional biocompatibilities. We investigated the uptake of phospholipid [polyethylene glycol (PEG), biotin, and folic acid terminated] modified CdSe/ZnS quantum dot micelles by cancer cells and its photostability under ultrviolet light in the C spectrum (UV-C) (254 nm) or UV-A (365 nm) light irradiation. The stability of micelles to the exposure of UV-C and UV-A light was assessed. Biotin-modified quantum dot micelles give photoluminescence enhancement under UV-C light irradiation. Folate modified micelle under UV-C and UV-A results show considerable photoluminescence enhancement. Photoluminescence lifetime measurements showed 7.04, 8.11 and 11.42 ns for PEG, folate, and biotin terminated phospholipid micelles, respectively. Folate and biotin-modified quantum dot micelles showed excellent uptake by HeLa cells under fluorescence confocal microscopy. Phospholipid CdSe/ZnS quantum dot micelles can be potentially used for diagnosis and treatment of cancer in the future.

Molecular Design of Zwitterionic Polymer Interfaces: Searching for the Difference

The widespread occurrence of zwitterionic compounds in nature has incited their frequent use in designing biomimetic materials. Therefore, zwitterionic polymers are a thriving field. A particular interest for this particular polymer class has currently focused on their use in establishing neutral, low-fouling surfaces. After highlighting strategies to prepare model zwitterionic surfaces as well as those that are more suitable for practical purposes relying strongly on radical polymerization methods, we present recent efforts to diversify the structure of the hitherto quite limited variety of zwitterionic monomers and of the derived polymers. We identify key structural variables, consider their influence on essential properties such as overall hydrophilicity and long-term stability, and discuss promising targets for the synthesis of new variants.

Romantic Surfaces: A Systematic Overview of Stable, Biospecific, and Antifouling Zwitterionic Surfaces

This Feature Article focuses on recent advances in the bioconjugation of surface-bound zwitterionic polymers for biospecific antifouling surfaces. Various approaches for the functionalization of antifouling zwitterionic polymers are systematically investigated, such as chain-end and side-chain functionalization. Side-chain functionalization methods can be further classified as those that are achieved through homopolymerization of custom-synthesized zwitterionic monomers equipped with reactive groups, or those that are achieved via synthesis of random or block copolymers combining different monomers with antifouling functionality and others with reactive groups. Several of the pros and cons of these approaches are outlined and discussed. Finally, some perspective and future directions of research are presented toward long-term stable, generically repelling surfaces that strongly and specifically adhere to a single component in a complex mixture.