An enzyme-responsive metal-enhanced near-infrared fluorescence sensor based on functionalized gold nanoparticles

Near-infrared (NIR) fluorescence imaging is promising due to the high penetration depths and minimal levels of autofluorescence in living systems. However, it suffers from low fluorescent quantum yield, and metal-enhanced fluorescence (MEF) is considered to be a promising technique to overcome this. Stimuli-responsive NIR fluorescence enhancement shows remarkable potential for applications in medical imaging and diagnosis. Herein, we successfully fabricated an enzyme-responsive near-infrared sensor based on MEF by functionalizing gold nanoparticles with NIR fluorophores and enzyme-responsive self-aggregation moieties. The NIR fluorescence of fluorophores on the gold nanoparticles was significantly enhanced due to increases both in the light scattering intensity and in the radiative decay rate (k _r) of the NIR fluorophores, along with relatively small variation in the nonradiative decay rate. This novel strategy for NIR fluorescent sensors should be particularly promising for NIR fluorescence imaging of enzyme activities and early diagnosis based on rationally designed nanomaterials.     

Stable Near-infrared-emitting Radical Nanoparticles for Fluorescence Imaging

Stable neutral luminescent radicals with unpaired electrons exhibit unique spin-allowed doublet-doublet transitions, which has attracted significant attention. Although they are pure organic molecules without metal ions thus thought to have low biological toxicity, the application of luminescent radicals to bioimaging has rarely been reported. Here, a stable radical with efficient near-infrared(NIR) emission and good photostability was designed and synthesized. After being wrapped into nanoparticles, it was applied to cell fluorescence imaging. The cytotoxicity experiments suggested that the nanoparticles have remarkable biocompatibility and excellent stability. An NIR fluorescent signal was successfully observed in the cytoplasm of HCT116 cells. The experimental results gave the first example of NIR emitting radical nanoparticles for cell fluorescence imaging and proved the feasibility of the application of luminescent radicals to fluorescence imaging.     

Preparation and Characterization of Uniform Near IR Polystyrene Nanoparticles

Biomaterials for in vivo fluorescence imaging are required to be biocompatible, nontoxic, photostable and highly fluorescent. Fluorescence must be in the near infrared (NIR) region of the electromagnetic spectrum to avoid absorption and autofluorescence of endogenous tissues. NIR fluorescent polystyrene nanoparticles may be considered ideal biomaterials for in vivo imaging applications. These NIR nanoparticles were prepared by a swelling process of polystyrene template nanoparticles with a hydrophobic NIR dye dissolved in a water‐miscible swelling solvent, a method developed for preparation of nonbiodegradable nanoparticles, for NIR fluorescent bioimaging applications. This method overcomes common problems that occur with dye entrapment during nanoparticle formation such as loss of fluorescence and size polydispersity. Fluorescence intensity of the nanoparticles was found to be size dependent, and was optimized for differently sized nanoparticles. The resulting NIR nanoparticles were also found to be more fluorescent and highly photostable compared to the free dye in solution, showing their potential as biomaterials for in vivo fluorescence imaging.     

CO2/NIR light dual-controlled nanoparticles for dsDNA unzipping

Both of carbon dioxide(CO2)and near-infrared(NIR)light as triggers for non-invasive remotely control are attracting wide attentions due to their good biocompatibility and easy operation.Here,CO2/NIR light dual controlled nanoparticles are proposed to remotely regulate the unzipping of dsDNA by using imidazole functionalized conjugated polymer nanoparticles(imidazole-CPNs).The dsDNA successfully coats on the shell of imidazole-CPNs to form imidazole-CPNs/dsDNA assembly due to intensively electrostatic interaction triggered by CO2.Furthermore,the unzipping process of dsDNA is remotely controlled by NIR light based on the photothermal effect,and it can be readily monitored by the fluorescence intensity of ethidium bromide(EB)and CD spectra of dsDNA.Thus,dual stimulation responsive imidazole-CPNs effectively control dsDNA unzipping under CO2 stimulus and NIR light,promising a new direction in the biological applications of DNA,such as the treatments of diseases caused by gene duplication abnormality.     

Dual-Targeting Biomimetic Semiconducting Polymer Nanocomposites for Amplified Theranostics of Bone Metastasis

Bone metastasis is a type of metastatic tumors that involves the spreads of malignant tumor cells into skeleton, and its diagnosis and treatment remain a big challenge due to the unique tumor microenvironment. We herein develop osteoclast and tumor cell dual-targeting biomimetic semiconducting polymer nanocomposites (SPFeN_OC) for amplified theranostics of bone metastasis. SPFeN_OC contain semiconducting polymer and iron oxide (Fe₃O₄) nanoparticles inside core and surface camouflaged hybrid membrane of cancer cells and osteoclasts. The hybrid membrane camouflage enables their targeting to both metastatic tumor cells and osteoclasts in bone metastasis through homologous targeting mechanism, thus achieving an enhanced nanoparticle accumulation in tumors. The semiconducting polymer mediates near-infrared (NIR) fluorescence imaging and sonodynamic therapy (SDT), and Fe₃O₄ nanoparticles are used for magnetic resonance (MR) imaging and chemodynamic therapy (CDT). Because both cancer cells and osteoclasts are killed synchronously via the combinational action of SDT and CDT, the vicious cycle in bone metastasis is broken to realize high antitumor efficacy. Therefore, 4T1 breast cancer-based bone metastasis can be effectively detected and cured by using SPFeN_OC as dual-targeting theranostic nanoagents. This study provides an unusual biomimetic nanoplatform that simultaneously targets osteoclasts and cancer cells for amplified theranostics of bone metastasis.     

Phosphorescent Polymeric Nanoparticles by Coordination Cross‐Linking as a Platform for Luminescence Imaging and Photodynamic Therapy

Water‐soluble phosphorescent polymeric nanoparticles with an average diameter of approximately 100 nm were synthesized by a coordination cross‐linking reaction. The pyridine blocks in poly(4‐vinyl pyridine‐b‐ethylene oxide) (P4VP‐b‐PEO) were cross‐linked by the iridium chloride‐bridged dimer in DMF solution. Owing to the presence of an iridium complex with different ligands in the core of the polymeric nanoparticles, NP‐1, NP‐2, and NP‐3 showed bright green, yellow, and red phosphorescence, respectively. PEG chains in the shell gave the polymeric nanoparticles solubility and biocompatibility, which was confirmed by an MTT assay using HeLa cells as a model cancer cell line. The flow cytometry and laser confocal fluorescence microscopy results revealed NP‐2, as an example, could be effectively uptaken by HeLa cells. Therefore, these polymeric nanoparticles can be used as luminescent probes for living cells. In addition, ¹O₂ could be effectively generated in the presence of NP‐2 upon irradiation with visible light (λ>400 nm, 300 mW cm^?2), which was confirmed by a clear decrease in the fluorescence intensity of 9,10‐dimethylanthracene (DMA). After incubation with NP‐2 at a concentration of 200 μg mL^?1 for 6 h, approximately 90 % of HeLa cells were effectively ablated upon irradiation with visible light for only 10 min, indicating the potential for photodynamic therapy with polymeric nanoparticles.     

Hyaluronic Acid/Poly(β‐Amino Ester) Polymer Nanogels for Cancer‐Cell‐Specific NIR Fluorescence Switch

Cancer‐cell‐specific pH‐activatable polymer nanogels consisting of CD44‐receptor‐targeting hyaluronic acid (HA), pH‐sensitive poly(β‐amino ester) (PBAE), and near‐infrared (NIR) fluorescent indocyanine green (ICG) were synthesized and used to detect cancer cells. The HA/PBAE/ICG‐polymer‐nanogel‐based NIR probe was nonfluorescent outside of tumor cells. After internalization by CD44‐receptor‐mediated endocytosis, the probe accumulated in the late endosomes or lysosomes where the acidic pH solubilized the PBAE and caused instant disassembly of the polymer nanogel. During endosomal maturation, the encapsulated ICG was released from its quenched state, inducing strong NIR fluorescence recovery. The nanogels generate a highly tumor‐specific NIR signal with a reduced background signal.     

A heterostructure composed of conjugated polymer and copper sulfide nanoparticles

A heterostructure formed by a conjugated polymer and semiconducting nanoparticles was produced. The conjugated polymer was synthesized by oxidative copolymerization of 3-thiopheneacetic acid and 3-hexylthiophene, thus obtaining an amphiphilic polythiophene that allows the formation of a stable polymer layer at the air-water interface. Different numbers of monolayers were deposited on solid substrates. CuS nanoparticles were grown directly in the polymeric matrix using the carboxylic groups as nucleation centers. The reactions were monitored by quartz crystal microbalance, Brewster angle, and fluorescence microscopy. The heterostructure showed increased conductivity as compared to the pristine polymer.     

Low power, biologically benign NIR light triggers polymer disassembly

Near infrared (NIR) irradiation can penetrate up to 10 cm deep into tissues and be remotely applied with high spatial and temporal precision. Despite its potential for various medical and biological applications, there is a dearth of biomaterials that are responsive at this wavelength region. Herein we report a polymeric material that is able to disassemble in response to biologically benign levels of NIR irradiation upon two-photon absorption. The design relies on the photolysis of the multiple pendant 4-bromo7-hydroxycoumarin protecting groups to trigger a cascade of cyclization and rearrangement reactions leading to the degradation of the polymer backbone. The new material undergoes a 50% Mw loss after 25 sec of ultraviolet (UV) irradiation by single photon absorption and 21 min of NIR irradiation via two-photon absorption. Most importantly, even NIR irradiation at biologically benign laser power is sufficient to cause significant polymer disassembly. Furthermore, this material is well tolerated by cells both before and after degradation. These results demonstrate for the first time a NIR sensitive material with potential to be used for in vivo applications.     

Near-infrared dyes,nanomaterials and proteins

Taking the advantage of reduced scattering and low autofluorescence background, the NIR fluorescence probes, such as fluorescence proteins, organic molecules and nanoparticles, not only hold the promise of in vivo imaging of biological processes in physiology and pathology with high signal-to-noise ratio, but also for clinical diagnosis. In this review, we provide an overview of the recent progress on NIR probes, focusing on fundamental mechanisms of NIR dyes and nanoparticles, and protein engineering strategies for NIR proteins.     

An Activatable Polymeric Reporter for Near-Infrared Fluorescent and Photoacoustic Imaging of Invasive Cancer

Discriminative detection of invasive and noninvasive breast cancers is crucial for their effective treatment and prognosis. However, activatable probes able to do so in vivo are rare. Herein, we report an activatable polymeric reporter (P-Dex) that specifically turns on near-infrared (NIR) fluorescent and photoacoustic (PA) signals in response to the urokinase-type plasminogen activator (uPA) overexpressed in invasive breast cancer. P-Dex has a renal-clearable dextran backbone that is linked with a NIR dye caged with an uPA-cleavable peptide substrate. Such a molecular design allows P-Dex to passively target tumors, activate NIR fluorescence and PA signals to effectively distinguish invasive MDA-MB-231 breast cancer from noninvasive MCF-7 breast cancer, and ultimately undergo renal clearance to minimize the toxicity potential. Thus, this polymeric reporter holds great promise for the early detection of malignant breast cancer.     

Near-infrared dyes,nanomaterials and proteins

Near-infrared probes including dyes, nanoparticles and proteins have been particularly useful for in vivo imaging because of their ability to penetrate tissue deeper with minimal scattering and autofluorescence, opening the door to study cell biology in physiological conditions.     

Supramolecular Assemblies with Near‐Infrared Emission Mediated in Two Stages by Cucurbituril and Amphiphilic Calixarene for Lysosome‐Targeted Cell Imaging

A two‐stage mediated near‐infrared (NIR) emissive supramolecular assembly for lysosome‐targeted cell imaging is presented. 4,4′‐Anthracene‐9,10‐diylbis(ethene‐2,1‐diyl))bis(1‐ethylpyridin‐1‐ium) bromide (ENDT) was synthesized as an organic dye with weak fluorescence emission at 625 nm. When ENDT complexes with cucurbit[8]uril (CB[8]), this binary supramolecular complex assembles into nanorods with a near‐infrared fluorescence emission (655 nm) and fluorescence enhancement as the first stage. Such supramolecular complexes interact with lower‐rim dodecyl‐modified sulfonatocalix[4]arene (SC4AD) to form nanoparticles for further fluorescence enhancement as the second stage. Furthermore, based on a co‐staining experiment with LysoTracker Blue, such nanoparticles can be applied in NIR lysosome‐targeted cell imaging.     

An Activatable Polymeric Reporter for Near‐Infrared Fluorescent and Photoacoustic Imaging of Invasive Cancer

Discriminative detection of invasive and noninvasive breast cancers is crucial for their effective treatment and prognosis. However, activatable probes able to do so in vivo are rare. Herein, we report an activatable polymeric reporter (P‐Dex) that specifically turns on near‐infrared (NIR) fluorescent and photoacoustic (PA) signals in response to the urokinase‐type plasminogen activator (uPA) overexpressed in invasive breast cancer. P‐Dex has a renal‐clearable dextran backbone that is linked with a NIR dye caged with an uPA‐cleavable peptide substrate. Such a molecular design allows P‐Dex to passively target tumors, activate NIR fluorescence and PA signals to effectively distinguish invasive MDA‐MB‐231 breast cancer from noninvasive MCF‐7 breast cancer, and ultimately undergo renal clearance to minimize the toxicity potential. Thus, this polymeric reporter holds great promise for the early detection of malignant breast cancer.     

Antibacterial polyethylene - Ethylene vinyl acetate polymeric blend by incorporation of zinc oxide nanoparticles

In this work, a Low-Density Polyethylene (LDPE) - Ethylene Vinyl Acetate (EVA) polymeric blend with antimicrobial activity was obtained. The main objective was to develop an antibacterial LDPE-EVA polymeric blend from the incorporation of antibacterial nanoparticles to increase the antimicrobial and sanitary safety of this polymeric blend when applied in the manufacture of medical products. The antibacterial activity was obtained from the incorporation of zinc oxide nanoparticles (ZnO-NPs) in the LDPE-EVA polymeric blends and the thermal properties were evaluated by differential scanning calorimetry and the mechanical properties by tensile stress tests for different percentages of ZnO-NPs. Scanning electron microscopy was used to study the morphological characteristics of the ZnO-NPs and also the characteristics of the distribution of nanoparticles in the polymer blends. The dispersive energy of x-ray fluorescence spectroscopy was used to study the chemical composition of the nanoparticles. Microbiological tests were performed to evaluate the antibacterial activity of the LDPE-EVA polymeric blends without and with ZnO-NPs against the bacteria Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative). The results obtained were excellent for the future application of the antibacterial LDPE-EVA polymeric blends to the manufacture of medical products. The Young's modulus values decreased and the tensile strength values showed small reductions and the thermal properties of the LDPE-EVA were not modified. However, the antibacterial activity of LDPE-EVA with 4 wt% of ZnO-NPs was excellent, eliminating the gram-positive bacteria in just 2 h and the gram-negative bacteria in just 2.5 h on their surfaces.     

Semiconducting Polymer Dots with Dual‐Enhanced NIR‐IIa Fluorescence for Through‐Skull Mouse‐Brain Imaging

Fluorescence probes in the NIR‐IIa region show drastically improved imaging owing to the reduced photon scattering and autofluorescence in biological tissues. Now, NIR‐IIa polymer dots (Pdots) are developed with a dual fluorescence enhancement mechanism. First, the aggregation induced emission of phenothiazine was used to reduce the nonradiative decay pathways of the polymers in condensed states. Second, fluorescence quenching was minimized by different levels of steric hindrance to further boost the fluorescence. The resulting Pdots displayed a fluorescence QY of ca. 1.7 % in aqueous solution, suggesting an enhancement of ca. 21 times in comparison with the original polymer in tetrahydrofuran (THF) solution. Small‐animal imaging by using the NIR‐IIa Pdots exhibited a remarkable improvement in penetration depth and signal to background ratio, as confirmed by through‐skull and through‐scalp fluorescent imaging of the cerebral vasculature of live mice.     

Reversible two-photon photoswitching and two-photon imaging of immunofunctionalized nanoparticles targeted to cancer cells

Both photoswitchable fluorescent nanoparticles and photoactivatable fluorescent proteins have been used for super-resolution far-field imaging on the nanometer scale, but the photoactivating wavelength for such photochemical events generally falls in the near-UV (NUV) region (<420 nm), which is not preferred in cellular imaging. However, using two near-IR (NIR) photons that are lower in energy, we can circumvent such problems and replace NUV single-photon excitations (e.g., 390 nm) with NIR two-photon excitations (e.g., 780 nm). Thus, we have demonstrated that alternating 780 nm NIR two-photon and 488 nm single-photon excitations induces reversible on-off fluorescence switching of immunotargeted nanoparticles in the human breast cancer cell line SK-BR-3. Herein, two-photon absorption not only caused spiropyran-merocyanine photoisomerization within the particles but also imparted red fluorescence. In comparison with single-photon NUV excitations, two-photon NIR laser excitations can potentially reduce absorption-related photodamage to living systems because cellular systems absorb much more weakly in the NIR.     

Silica-coated gold nanostars for combined surface-enhanced Raman scattering (SERS) detection and singlet-oxygen generation: a potential nanoplatform for theranostics

This paper reports the synthesis and characterization of surface-enhanced Raman scattering (SERS) label-tagged gold nanostars, coated with a silica shell containing methylene blue photosensitizing drug for singlet-oxygen generation. To our knowledge, this is the first report of nanocomposites possessing a combined capability for SERS detection and singlet-oxygen generation for photodynamic therapy. The gold nanostars were tuned for maximal absorption in the near-infrared (NIR) spectral region and tagged with a NIR dye for surface-enhanced resonance Raman scattering (SERRS). Silica coating was used to encapsulate the photosensitizer methylene blue in a shell around the nanoparticles. Upon 785 nm excitation, SERS from the Raman dye is observed, while excitation at 633 nm shows fluorescence from methylene blue. Methylene-blue-encapsulated nanoparticles show a significant increase in singlet-oxygen generation as compared to nanoparticles synthesized without methylene blue. This increased singlet-oxygen generation shows a cytotoxic effect on BT549 breast cancer cells upon laser irradiation. The combination of SERS detection (diagnostic) and singlet-oxygen generation (therapeutic) into a single platform provides a potential theranostic agent.     

An aqueous photo-controlled polymerization under NIR wavelengths: synthesis of polymeric nanoparticles through thick barriers

We report an aqueous and near-infrared (NIR) light mediated photoinduced reversible addition–fragmentation chain transfer (photo-RAFT) polymerization system using tetrasulfonated zinc phthalocyanine (ZnPcS₄⁻) as a photocatalyst. Owing to the high catalytic efficiency and excellent oxygen tolerance of this system, well-controlled polyacrylamides, polyacrylates, and polymethacrylates were synthesized at fast rates without requiring deoxygenation. Notably, NIR wavelengths possess enhanced light penetration through non-transparent barriers compared to UV and visible light, allowing high polymerization rates through barriers. Using 6.0 mm pig skin as a barrier, the polymerization rate was only reduced from 0.36 to 0.21 h⁻¹, indicating potential for biomedical applications. Furthermore, longer wavelengths (higher λ) can be considered an ideal light source for dispersion photopolymerization, especially for the synthesis of large diameter (d) nanoparticles, as light scattering is proportional to d⁶/λ⁴. Therefore, this aqueous photo-RAFT system was applied to photoinduced polymerization-induced self-assembly (photo-PISA), enabling the synthesis of polymeric nanoparticles with various morphologies, including spheres, worms, and vesicles. Taking advantage of high penetration and reduced light scattering of NIR wavelengths, we demonstrate the first syntheses of polymeric nanoparticles with consistent morphologies through thick barriers.

Taking advantage of high penetration and reduced light scattering of NIR wavelengths, we demonstrate the syntheses of polymeric nanoparticles with consistent morphologies through thick barriers.     

Surface-modulated and thermoresponsive polyphosphoesternanoparticles for enhanced intracellular drug delivery

The chemical structure of end groups influenced the phase transition temperature of thermoresponsive polymers. We demonstrated a strategy for the preparation of the pH/thermo-responsive polymeric nanoparticles via subtle modification of end groups of thermoresponsive polymer segments with a carboxyl group and revealed its potential application for enhanced intracellular drug delivery. By developing a polymeric nanoparticle composed of poly(aliphatic ester) as the inner core and thermoresponsive polyphosphoester as the outer shell, we showed that end groups of thermoresponsive polyphosphoester segments modified by carboxyl groups exhibited a pH/thermo-responsive behavior due to the hydrophilic to hydrophobic transitions of the end groups in response to the pH. Moreover, by encapsulating doxorubicin into the hydrophobic core of such pH/thermo-responsive polymer nanoparticles, their intracellular delivery and cytotoxicity to wild-type and drug-resistant tumor cells were significantly enhanced through the phase-transition-dependent drug release that was triggered by endosomal/lysosomal pH. This novel strategy and the multi-responsive polymer nanoparticles achieved by the subtle chain-terminal modification of thermoresponsive polymers provide a smart platform for biomedical applications.