A surface energy transfer nanoruler for measuring binding site distances on live cell surfaces

Molecular Force Sensors for Biological Application

The mechanical forces exerted by cells on their surrounding microenvironment are known as cellular traction forces. These forces play crucial roles in various biological processes, such as tissue development, wound healing and cell functions. However, it is hard for traditional techniques to measure cellular traction forces accurately because their magnitude (from pN to nN) and the length scales over which they occur (from nm to μm) are extremely small. In order to fully understand mechanotransduction, highly sensitive tools for measuring cellular forces are needed. Current powerful techniques for measuring traction forces include traction force microscopy (TFM) and fluorescent molecular force sensors (FMFS). In this review, we elucidate the force imaging principles of TFM and FMFS. Then we highlight the application of FMFS in a variety of biological processes and offer our perspectives and insights into the potential applications of FMFS.

Single-Nucleobase-Resolved Nanoruler Determines the Surface Energy Transfer Radius on the Living Cell Membrane

Investigations about surface energy transfer radius (r0) are limited to the aqueous solution system, and it is quite limited on experimental values of r0 between dyes and the corresponding gold particle (AuNP) sizes, especially for living cell systems. Hence, the selection of suitable AuNP-dye pairs is restricted when designing nanometal surface energy transfer (NSET) strategies in analytical sciences. Here, we developed a single-nucleobase-resolved NSET strategy to in situ measure the r0 value between a specific dye and different-sized AuNPs on the living cell membrane. Using the aptamer-dye complex (XQ-2d-nTA-FAM) and antiCD71 antibody-coupled AuNP conjugate (Au@antiCD71) as two working elements to bind two different sites on CD71 receptors on living cell membranes, we modified the nTA spacer between FAM and the terminal of aptamer to change the distance (r) from FAM to AuNP center and further adjusted the quenching efficiency (Φ) between them. Different r0 values of various AuNP-FAM pairs in living cells are determined by this in situ detection strategy. Based on this single-nucleobase-resolved NSET strategy, we established a simple and efficient universal method for measuring r0 in the living cell system, which greatly expanded the selection range of AuNP-dye pairs during the construction of the NSET model at the nanoscale.

Record Resolution of Nanometal Surface Energy Transfer Optical Nanoruler Projects 3D Spatial Configuration of Aptamers on a Living Cell Membrane

Decrypting the in situ three-dimensional spatial configuration of an aptamer is of considerable significance; however, suitable nanoscale resolution tools are lacking. Herein, we show that a new nanometal surface energy transfer (NSET) optical nanoruler has a record resolution, down to single-nucleobase levels. We labeled fluorophores on different T bases of XQ-2d, including 5', 3', 6T, 22T, 38T, and 52T positions. The NSET nanoruler in situ decrypted the base sequence-dependent distance projection on the nanogold surface, demonstrating that 5', 3', stem, and loop structures are symmetrical in three-dimensional spatial configuration. The orientation of the 5' and 3' stem was toward the antiCD71-binding site, whereas the loop was in the opposite direction at a considerable distance. Molecular docking simulation was performed to list all of the possible conformations; however, all base distance parameters projecting on the nanogold surface determined a single conformation of XQ-2d. The specific binding sites of XQ-2d were Lys477, Ser691, and Arg698 on the CD71 receptor.

Compartmentalized drug localization studies in extracellular vesicles for anticancer therapy

In the development of therapeutic extracellular vesicles (EVs), drug encapsulation efficiencies are significantly lower when compared with synthetic nanomedicines. This is due to the hierarchical structure of the EV membrane and the physicochemical properties of the candidate drug (molecular weight, hydrophilicity, lipophilicity, and so on). As a proof of concept, here we demonstrated the importance of drug compartmentalization in EVs as an additional parameter affecting the therapeutic potential of drug-loaded EVs. In human adipose mesenchymal stem cell (hADSC) derived EVs, we performed a comparative drug loading analysis using two formulations of the same chemotherapeutic molecule - free doxorubicin (DOX) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) lipid-conjugated doxorubicin (L-DOX) - to enhance the intracellular uptake and therapeutic efficacy. By nano surface energy transfer (NSET) and molecular simulation techniques, along with cryo-TEM analysis, we confirmed the differential compartmentalization of these two molecules in hADSC EVs. L-DOX was preferentially adsorbed onto the surface of the EV, due to its higher lipophilicity, whereas free DOX was mostly encapsulated within the EV core. Also, the L-DOX loaded EV (LDOX@EV) returned an almost three-fold higher DOX content as compared to the free DOX loaded EV (DOX@EV), for a given input mass of drug. Based on the cellular investigations, L-DOX@EV showed higher cell internalization than DOX@EV. Also, in comparison with free L-DOX, the magnitude of therapeutic potential enhancement displayed by the surface compartmentalized L-DOX@EV is highly promising and can be exploited to overcome the sensitivity of many potential drugs, which are impermeable in nature. Overall, this study illustrates the significance of drug compartmentalization in EVs and how this could affect intracellular delivery, loading efficiency, and therapeutic effect. This will further lay the foundation for the future systematic investigation of EV-based biotherapeutic delivery platforms for personalized medicine.

Assessment of biomass-derived carbon dots as highly sensitive and selective templates for the sensing of hazardous ions

Access to safe drinking water and a hygienic living environment are the basic necessities that encourage healthy living. However, the presence of various pollutants (especially toxic heavy metal ions) at high concentrations in water renders water unfit for drinking and domestic use. The presence of high concentrations of heavy-metal ions (e.g., Pb2+, Hg2+, Cr6+, Cd2+, or Cu2+) greater than their permissible limits adversely affects human health, and increases the risk of cancer of the kidneys, liver, skin, and central nervous system. Therefore, their detection in water is crucial. Due to the various benefits of "green"-synthesized carbon-dots (C-dots) over other materials, these materials are potential candidates for sensing of toxic heavy-metal ions in water sources. C-dots are very small carbon-based nanomaterials that show chemical stability, magnificent biocompatibility, excitation wavelength-dependent photoluminescence (PL), water solubility, simple preparation strategies, photoinduced electron transfer, and the opportunity for functionalization. A new family of C-dots called "carbon quantum dots" (CQDs) are fluorescent zero-dimensional carbon nanoparticles of size < 10 nm. The green synthesis of C-dots has numerous advantages over conventional chemical routes, such as utilization of inexpensive and non-poisonous materials, straightforward operations, rapid reactions, and renewable precursors. Natural sources, such as biomass and biomass wastes, are broadly accepted as green precursors for fabricating C-dots because these sources are economical, ecological, and readily/extensively accessible. Two main methods are available for C-dots production: top-down and bottom-up. Herein, this review article discusses the recent advancements in the green fabrication of C-dots: photostability; surface structure and functionalization; potential applications for the sensing of hazardous anions and toxic heavy-metal ions; binding of toxic ions with C-dots; probable mechanistic routes of PL-based sensing of toxic heavy-metal ions. The green production of C-dots and their promising applications in the sensing of hazardous ions discussed herein provides deep insights into the safety of human health and the environment. Nonetheless, this review article provides a resource for the conversion of low-value biomass and biomass waste into valuable materials (i.e., C-dots) for promising sensing applications.

Principles and Applications of Resonance Energy Transfer Involving Noble Metallic Nanoparticles

Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, strong surface plasmon resonance absorption and local electric field enhancement are generated near noble metallic nanoparticles, and the resulting energy transfer shows potential applications in microlasers, quantum information storage devices and micro-/nanoprocessing. In this review, we present the basic principle of the characteristics of noble metallic nanoparticles, as well as the representative progress in resonance energy transfer involving noble metallic nanoparticles, such as fluorescence resonance energy transfer, nanometal surface energy transfer, plasmon-induced resonance energy transfer, metal-enhanced fluorescence, surface-enhanced Raman scattering and cascade energy transfer. We end this review with an outlook on the development and applications of the transfer process. This will offer theoretical guidance for further optical methods in distance distribution analysis and microscopic detection.

Ligand Dilution Analysis Facilitates Aptamer Binding Characterization at the Single-Molecule Level

Cell-specific aptamers offer a powerful tool to study membrane receptors at the single-molecule level. Most target receptors of aptamers are highly expressed on the cell surface, but difficult to analyze in situ because of dense distribution and fast velocity. Therefore, we herein propose a random sampling-based analysis strategy termed ligand dilution analysis (LDA) for easily implemented aptamer-based receptor study. Receptor density on the cell surface can be calculated based on a regression model. By using a synergistic ligand dilution design, colocalization and differentiation of aptamer and monoclonal antibody (mAb) binding on a single receptor can be realized. Once this is accomplished, precise binding site and detailed aptamer-receptor binding mode can be further determined using molecular docking and molecular dynamics simulation. The ligand dilution strategy also sets the stage for an aptamer-based dynamics analysis of two- and three-dimensional motion and fluctuation of highly expressed receptors on the live cell membrane.

Carbon Dot Emission Enhancement in Covalent Complexes with Plasmonic Metal Nanoparticles

Carbon dots can be used for the fabrication of colloidal multi-purpose complexes for sensing and bio-visualization due to their easy and scalable synthesis, control of their spectral responses over a wide spectral range, and possibility of surface functionalization to meet the application task. Here, we developed a chemical protocol of colloidal complex formation via covalent bonding between carbon dots and plasmonic metal nanoparticles in order to influence and improve their fluorescence. We demonstrate how interactions between carbon dots and metal nanoparticles in the formed complexes, and thus their optical responses, depend on the type of bonds between particles, the architecture of the complexes, and the degree of overlapping of absorption and emission of carbon dots with the plasmon resonance of metals. For the most optimized architecture, emission enhancement reaching up to 5.4- and 4.9-fold for complexes with silver and gold nanoparticles has been achieved, respectively. Our study expands the toolkit of functional materials based on carbon dots for applications in photonics and biomedicine to photonics.

An ultrasensitive detection platform for cocaine: Aptasensing strategy in capillary tube

Cocaine as a detrimental addictive drug threats human health through inducing heart problem, blood pressure, anxiety, immunodeficiency, paranoia, and organ damage. Thus, the quantification of cocaine in the biological samples by a simple, high specificity, and fast method is highly urgent to decrease the harmful effect of the misuse of this drug. In this study, we constructed a novel fluorescent aptasensor by combining the fluorescein (FAM)-modified specific aptamer and AuNPs in a capillary tube as the sensing substrate for the first time. The presence of cocaine recovered the fluorescence response of the aptasensor through interaction with the aptamer and differentiation of the aptamer@AuNPs complex. By fluorescence microscopy imaging of the aptasensor substrate and its quantitative analysis, a remarkable linear range from 100 pM to 600 µM and the ultra-low limit of detection (LOD) as 0.31 pM were achieved for the target detection. Cocaine was successfully quantified in the real samples (human serum and urine) by using the aptasensor. The aptasensor is simple, easy-to-use, favorable applicability, and cost-effective; and to the best of our knowledge, it is the first use of the capillary tube as a sensing platform just by using about 3 μl of the samples. It is also an easy-to-carry tool, promising for the on-site target detection. Besides, it can be a portable device for monitoring cocaine by using a handheld single-beam fluorescence microscope. It can be an appropriate detection tool in forensic science and medicine.

Color Conversion Light-Emitting Diodes Based on Carbon Dots: A Review

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow-green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity.

Combined Effects of Emitter-Emitter and Emitter-Plasmonic Surface Separations Dictate Photoluminescence Enhancement in Plasmonic Field

The brightness of an emitter can be enhanced by metal-enhanced fluorescence, wherein the excitonic dipole couples with the electromagnetic field of the surface plasmon. Herein, we experimentally map the landscape...

Sulfhydryl functionalized carbon quantum dots as a turn-off fluorescent probe for sensitive detection of Hg2

Mercury ion (Hg2+) is one of the most toxic heavy metal ions and lowering the detection limit of Hg2+ is always a challenge in analytical chemistry and environmental analysis. In this work, sulfhydryl functionalized carbon quantum dots (HS-CQDs) were synthesized through a one-pot hydrothermal method. The obtained HS-CQDs were able to detect mercury ions Hg2+ rapidly and sensitively through fluorescence quenching, which may be ascribed to the formation of nonfluorescent ground-state complexes and electron transfer reaction between HS-CQDs and Hg2+. A modification of the HS-CQD surface by -SH was confirmed using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The HS-CQDs sensing system obtained a good linear relationship over a Hg2+ concentration ranging from 0.45 μM to 2.1 μM with a detection limit of 12 nM. Delightfully, the sensor has been successfully used to detect Hg2+ in real samples with satisfactory results. This means that the sensor has the potential to be used for testing actual samples.

Cell surface-localized imaging and sensing

Systematically dissecting the molecular basis of the cell surface as well as its related biological activities is considered as one of the most cutting-edge fields in fundamental sciences. The advent of various advanced cell imaging techniques allows us to gain a glimpse of how the cell surface is structured and coordinated with other cellular components to respond to intracellular signals and environmental stimuli. Nowadays, cell surface-related studies have entered a new era featured by a redirected aim of not just understanding but artificially manipulating/remodeling the cell surface properties. To meet this goal, biologists and chemists are intensely engaged in developing more maneuverable cell surface labeling strategies by exploiting the cell's intrinsic biosynthetic machinery or direct chemical/physical binding methods for imaging, sensing, and biomedical applications. In this review, we summarize the recent advances that focus on the visualization of various cell surface structures/dynamics and accurate monitoring of the microenvironment of the cell surface. Future challenges and opportunities in these fields are discussed, and the importance of cell surface-based studies is highlighted.

Elucidating the Quenching Mechanism in Carbon Dot-Metal Interactions-Designing Sensitive and Selective Optical Probes

Overexposure to metals has significant adverse effects on human and animal health coupled with nefarious consequences to the environment. Sensitive tools to measure low contaminant levels exist, but often come at a high cost and require tedious procedures. Thus, there exists a need for the development of affordable metal sensors that can offer high sensitivity and selectivity while being accessible on a global scale. Here, carbon dots, prepared in a one-pot synthesis using glutathione and formamide, have been developed as dual fluorescent metal sensing probes. Following extensive characterization of their physico-chemical properties, it is demonstrated that dual fluorescence can be exploited to build a robust ratiometric sensor with low-ppb detection sensitivity in water. This investigation shows that these optical probes are selective for Pb2+ and Hg2+ ions. Using steady-state and dynamic optical characterization techniques, coupled with hard and soft acid-base theory, the underlying reason for this selective behavior was identified. These findings shed light on the nature of metal-carbon dot interactions, which can be used to tailor their properties to target specific metal ions. Finally, these findings can be applicable to other fluorescent nanoparticle systems that are targeted for development as metal sensors.

Natural tripeptide capped pH-sensitive gold nanoparticles for efficacious doxorubicin delivery both in vitro and in vivo

Nanobiotechnology has been gaining ever-increasing interest for the successful implementation of chemotherapy based treatment of cancer. Gold nanoparticles (AuNPs) capped with a natural pH-responsive short tripeptide (Lys-Phe-Gly or KFG) sequence are presented herein for significant intracellular delivery of an anti-cancer drug, doxorubicin (DOX). A particularly increased apoptotic response has been observed for DOX treatments mediated by KFG-AuNPs when compared with drug alone treatments in various cell lines (BT-474, HeLa, HEK 293 T and U251). Furthermore, KFG-AuNP mediated DOX treatment significantly decreases cell proliferation and tumor growth in a BT-474 cell xenograft model in nude mice. In addition, KFG-AuNPs demonstrate efficacious drug delivery in DOX-resistant HeLa cells (HeLa-DOXR).

High-sensitive imprinted membranes based on surface-enhanced Raman scattering for selective detection of antibiotics in water

Poly(vinylidene fluoride) (PVDF) is known as one of the widely used membrane separation materials with excellent physical and chemical properties. In this work, we combine surface-enhanced Raman scattering (SERS) detection technology, membrane separation technology and molecular imprinting technology (MIT) to improve sensitivity and selectivity for selective detection of the enrofloxacin hydrochloride in water. In this investigation, PVDF membranes were used as the support materials and different experiment parameters were investigated to obtain the best property. Meanwhile, the Ag nanoparticles (Ag NPs) modified by 3-methacryloxypropyltrimethoxysilane (KH-570) were used as the SERS substrates and they were uniformly dispersed on the surface of the membrane. Finally, Ag-based SERS imprinted membranes (ASIMs) with specific recognition property were successfully prepared with enrofloxacin hydrochloride as the template molecule, acrylamide (AM) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker agent and 2,2'-azobis(2-methylpropionitrile) (AIBN) as the initiator by a facile and versatile precipitation polymerization strategy. Under the optimal condition, it was presented good linear relationship (R² = 0.994) between the Raman signal (at 1390.8 cm^-1) and the concentration (10^-3 mol·L^-1-10^-7 mol·L^-1) of the templates, and the limit of detection was determined as 10^-7 mol·L^-1. The morphology and characters were investigated and the results proved that the SERS imprinted membranes could be used into the selective detection of antibiotics and it provided a novel approach of antibiotics detection.

Elucidation and Structural Modeling of CD71 as a Molecular Target for Cell-Specific Aptamer Binding

Pancreatic cancer is a highly lethal malignancy associated with tissues of the pancreas. Early diagnosis and effective treatment are crucial to improving the survival rate of patients with pancreatic cancer. In a previous study, we employed the cell-SELEX strategy to obtain an ssDNA aptamer termed XQ-2d with high binding affinity for pancreatic cancer. Here, we first identify CD71 as the XQ-2d-binding target. We found that knockdown of CD71 abolished the binding of XQ-2d and that the binding affinity of XQ-2d is associated with membrane-bound CD71, rather than total CD71 levels. Competitive analysis revealed that XQ-2d shares the same binding site on CD71 with transferrin (Tf), but not anti-CD71 antibody. We then used a surface energy transfer (SET) nanoruler to measure the distance between the binding sites of XQ-2d and anti-CD71 antibody, and it was about 15 nm. Furthermore, we did molecular dynamics simulation to clarify that the spatial structure of XQ-2d and Tf competitively binding to CD71. We also engineered XQ-2d-mediated targeted therapy for pancreatic cancer, using an XQ-2d-based complex for loading doxorubicin (Dox). Because CD71 is overexpressed not only in pancreatic cancer but also in a variety of tumors, our work provides a systematic novel way of studying a potential biomarker and also promising tools for cancer diagnosis and therapy, opening new doors for effective cancer theranostics.

Rational design of multimodal therapeutic nanosystems for effective inhibition of tumor growth and metastasis

Simultaneous inhibition of both tumor growth and metastasis is the key to treating metastatic cancer, yet the development of effective drug delivery systems represents a great challenge since multimodal therapeutic agents must be rationally combined to overcome the biological mechanisms underpinning tumor cell proliferation and invasion. In this context, we report a hybrid therapeutic nanoscale platform that incorporates an anti-proliferative drug, doxorubicin (DOX), and an anti-NF-κB agent, p65-shRNA, for effective treatment of metastatic breast cancer. In our design, we first conjugated DOX via an acid-labile linker onto gold nanorods that were pre-modified with the tumor targeting peptide RGD and a positively charged, disulfide cross-linked short polyethylenimines (DSPEI), and then incorporated shRNA through electrostatic complexation with DSPEI. We show that this "all in one" nanotherapeutic system (RDG/shRNA@DOX) can be effectively internalized through RGD-mediated endocytosis, followed by stimuli-responsive intracellular co-release of DOX and shRNA. Our in vitro experiments suggest that this multimodal system can significantly inhibit cell proliferation, angiogenesis, and invasion of metastatic MDA-MB-435 cancer cells. Systemic administration of RDG/shRNA@DOX into a metastatic mouse model led to enhanced tumor accumulation, and, most importantly, significant inhibition of in situ tumor growth and almost complete suppression of tumor metastasis. We believe this hybrid multimodal nanotherapeutic system provides important insight into the rational design of therapeutic systems for the effective treatment of metastatic carcinoma.

STATEMENT OF SIGNIFICANCE

The key to successfully treat metastatic cancer is the simultaneous inhibition of both tumor growth and metastasis. This represents a great challenge for the design of drug delivery systems since multimodal therapeutic agents must be rationally combined to overcome the respective biological mechanisms underpinning tumor cell proliferation and invasion. Toward this end, we developed a hybrid nanomedicine platform that incorporates an anti-proliferative drug, doxorubicin (DOX), and an anti-NF-κB agent, p65-shRNA, for effective treatment of metastatic breast cancer. We showed that this multimodal system (RDG/shRNA@DOX) enhanced tumor accumulation, led to prolonged circulation, and most importantly, significant inhibition of in situ tumor growth and almost complete suppression of tumor metastasis. We believe this hybrid multimodal nanotherapeutic system provides significant insight into the rational design of therapeutic systems for the effective treatment of metastatic cancer.

Nanosensing of ATP by fluorescence recovery after surface energy transfer between rhodamine B and curcubit[7]uril-capped gold nanoparticles

The authors describe a method for functionalization of gold nanoparticles (AuNPs) with the supramolecular host molecule, curcubit[7]uril (CB[7]) which can bind rhodamine B (RhB). The fluorescence of RhB is quenched by the AuNPs via surface energy transfer. On addition of ATP, a dimeric RhB-ATP complex is formed and RhB is pushed out of CB[7]. Hence, fluorescence increases by a factor of 8. This fluorescence recovery effect has been utilized to develop a new detection scheme for ATP. The assay, measured at fluorescence excitation and emission wavelengths of 500 nm and 574 nm respectively, works in the 0.5-10 μM concentration range and has a 100 nM detection limit. The method is not interfered by UTP, GTP, CTP, TTP, ascorbic acid and glutathione. Graphical abstract Schematic of a method for determination of ATP in the 500 nM to 10 μM concentration range by using fluorescence recovery after surface energy transfer (SET) between rhodamine B (RhB) and gold nanoparticles capped with curcubit[7]uril (CB[7]).

Sub-Angstrom Gold Nanoparticle/Liposome Interfaces Controlled by Halides

A hallmark of nanoscience is size-dependent and distance-dependent physical properties. Although most previous studies focused on optical properties, which are often tuned at nanometer scale, we herein report on the interaction between halide-capped gold nanoparticles (AuNPs) and phosphocholine (PC) liposomes at the sub-Angstrom level. Halide-capped AuNPs are adsorbed by PC liposomes attributable to van der Waals force. Iodide-capped AuNPs interact much more weakly with the liposomes compared with bromide- and chloride-capped AuNPs, as indicated by a liposome leakage assay and differential scanning calorimetry. This is explained by the slightly larger size of iodide separating the AuNP core more from the liposome surface. Cryo-transmission electron microscopy indicates that the liposomes remain intact when mixed with these halide-capped AuNPs of 13 or 70 nm in diameter. Other even larger ligands, including small thiol compounds, DNA oligonucleotides, proteins, and polymers, fully blocked the interaction, whereas AuNPs dispersed in noninteracting ions, including fluoride, phosphate, perchlorate, nitrate, sulfate, and bicarbonate, are still adsorbed strongly by 1,2-dioleoyl- sn-glycero-3-phosphocholine liposomes. Taken together, halides can be used to control interparticle distances at an extremely small scale with remarkable effects on materials properties, allowing surface probing, biosensor development, and fundamental surface science studies.

Precision engineering of targeted nanocarriers

Since their introduction in 1980, the number of advanced targeted nanocarrier systems has grown considerably. Nanocarriers capable of targeting single receptors, multiple receptors, or multiple epitopes have all been used to enhance delivery efficiency and selectivity. Despite tremendous progress, preclinical studies and clinically translatable nanotechnology remain disconnected. The disconnect in targeting efficacy may stem from poorly-understood factors such as receptor clustering, spatial control of targeting ligands, ligand mobility, and ligand architecture. Further, the relationship between receptor distribution and ligand architecture remains elusive. Traditionally, targeted nanocarriers were engineered assuming a "static" target. However, it is becoming increasingly clear that receptor expression patterns change in response to external stimuli and disease progression. Here, we discuss how cutting-edge technologies will enable a better characterization of the spatiotemporal distribution of membrane receptors and their clustering. We further describe how this will enable the design of new nanocarriers that selectively target the site of disease. Ultimately, we explore how the precision engineering of targeted nanocarriers that adapt to receptor dynamics will have the potential to drive nanotechnology to the forefront of therapy and make targeted nanomedicine a clinical reality. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Lipid-Based Structures Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Enhanced distance-dependent fluorescence quenching using size tuneable core shell silica nanoparticles

Core–shell silica nanoparticles were shown to demonstrate quenching between a fluorescent core and surface black hole quencher layer, separated by a size controllable silica shell.

Concentration-dependent photophysical switching in mixed self-assembled monolayers of pentacene and perylenediimide on gold nanoclusters

The precise control and switching of photophysical processes such as singlet fission, electron transfer and excimer were performed using mixed SAMs of pentacene and perylenediimide units on Au nanoclusters.

Photo-responsive camptothecin-based polymeric prodrug coated silver nanoparticles for drug release behaviour tracking via the nanomaterial surface energy transfer (NSET) effect

A photo-responsive hybrid drug delivery system for drug release behaviour tracking via the nanomaterial surface energy transfer (NSET) effect.

Silver Nanoparticles Covered with pH-Sensitive Camptothecin-Loaded Polymer Prodrugs: Switchable Fluorescence "Off" or "On" and Drug Delivery Dynamics in Living Cells

A unique drug delivery system, in which silver nanoparticles (AgNPs) are covered with camptothecin (CPT)-based polymer prodrug, has been developed, and the polymer prodrug, in which the CPT is linked to the polymer side chains via an acid-labile β-thiopropionate bond, is prepared by RAFT polymerization. For poly(2-(2-hydroxyethoxy)ethyl methacrylate-co-methacryloyloxy-3-thiahexanoyl-camptothecin)@AgNPs [P(HEO₂MA-co-MACPT)@AgNPs], the polymer thickness on the AgNP surface is around 5.9 nm (TGA method). In vitro tests in buffer solutions at pH = 7.4 reveal that fluorescence of the CPT in the hybrid nanoparticles is quenched due to the nanoparticle surface energy transfer (NSET) effect, but under acidic conditions, the CPT fluorescence is gradually recovered with gradual release of the CPT molecules from the hybrid nanoparticles through cleavage of the acid-labile bond. The NSET "on" and "off" is induced by the CPT-AgNP distance change. This unique property makes it possible to track the CPT delivery and release process from the hybrid nanoparticles in the living cells in a real-time manner. The internalization and intracellular releasing tests of the hybrid nanoparticles in the HeLa cells demonstrate that the lysosome containing the hybrid nanoparticles displays CPT blue fluorescence due to release of the CPT under acidic conditions, and the drug-releasing kinetics shows fluorescence increase of the released CPT with incubation time. The cytotoxicity of hybrid nanoparticles is dependent on activity of the acid-labile bond. Therefore, this is a potential efficient drug delivery system in cancer therapy and a useful approach to study the mechanism of release process in the cells.

Facile Assembly/Disassembly of DNA Nanostructures Anchored on Cell-Mimicking Giant Vesicles

DNA nanostructures assembled on living cell membranes have become powerful research tools. Synthetic lipid membranes have been used as a membrane model to study the dynamic behavior of DNA nanostructures on fluid soft lipid bilayers, but without the inherent complexity of natural membranes. Herein, we report the assembly and disassembly of DNA nanoprisms on cell-mimicking micrometer-scale giant membrane vesicles derived from living mammalian cells. Three-dimensional DNA nanoprisms with a DNA arm and a cholesterol anchor were efficiently localized on the membrane surface. The assembly and disassembly of DNA nanoprisms were dynamically manipulated by DNA strand hybridization and toehold-mediated strand displacement. Furthermore, the heterogeneity of reversible assembly/disassembly of DNA nanoprisms was monitored by Förster resonance energy transfer. This study suggests the feasibility of DNA-mediated functional biomolecular assembly on cell membranes for biomimetics studies and delivery systems.

Tumor cell capture patterns around aptamer-immobilized microposts in microfluidic devices

Circulating tumor cells (CTCs) have shown potential for cancer diagnosis and prognosis. Affinity-based CTC isolation methods have been proved to be efficient for CTC detection in clinical blood samples. One of the popular choices for affinity-based CTC isolation is to immobilize capture agents onto an array of microposts in microchannels, providing high CTC capture efficiency due to enhanced interactions between tumor cells and capture agents on the microposts. However, how the cells interact with microposts under different flow conditions and what kind of capture pattern results from the interactions have not been fully investigated; a full understanding of these interactions will help to design devices and choose experimental conditions for higher CTC capture effeciency. We report our study on their interaction and cell distribution patterns around microposts under different flow conditions. Human acute lymphoblastic leukemia cells (CCRF-CEM) were used as target cancer cells in this study, while the Sgc8 aptamer that has specific binding with CCRF-CEM cells was employed as a capture agent. We investigated the effects of flow rates and micropost shapes on the cell capture efficiency and capture patterns on microposts. While a higher flow rate decreased cell capture efficiency, we found that the capture pattern around microposts also changed, with much more cells captured in the front half of a micropost than at the back half. We also found the ratio of cells captured on microposts to the cells captured by both microposts and channel walls increased as a function of the flow rate. We compared circular microposts with an elliptical shape and found that the geometry affected the capture distribution around microposts. In addition, we have developed a theoretical model to simulate the interactions between tumor cells and micropost surfaces, and the simulation results are in agreement with our experimental observation.

Thermo-responsive molecularly imprinted sensor based on the surface-enhanced Raman scattering for selective detection of R6G in the water

In this study, a novel SERS sensor was successfully prepared by combining a molecular imprinted technique (MIT) with a SERS technique to improve the selectivity of the traditional SERS technique.

A high-performance SERS-imprinted sensor doped with silver particles of different surface morphologies for selective detection of pyrethroids in rivers

Ag-MIPs were prepared through a multistep procedure, in which MPS and LC were selected as the template molecules. These materials could selectively rebind the templates and could be detected using Raman spectroscopy.

Understanding the effect of size and shape of gold nanomaterials on nanometal surface energy transfer

Gold Nanomaterials (GNMs) interact with fluorophores via electromagnetic coupling under excitation. In this particular work we carried out (to the best of our knowledge for the first time) a comprehensive study of systematic quenching of a blue emitter 2-Anthracene Sulfonate (2-AS) in the presence of gold nanoparticles of different size and shape. We synthesized gold nanomaterials of four different dimensions [nanoparticle (0D), nanorod (1D), nanotriangle (2D) and nanobipyramids (3D)] and realized the underlying effect on the emitting dipole in terms of steady and time resolved fluorescence. Nanometal Surface Energy Transfer (NSET) has already been proved to be the best long range spectroscopic ruler so far. Many attempts have been made to understand the interaction between a fluorescent molecule and gold nanomaterials. But not a single model can interpret alone the interaction phenomena. We have opted three different models to compare the experimental and theoretical data. Due to the presence of size dependent absorptivity and dielectric function, modified CPS-Kuhn model was proved to be the worthiest to comprehend variance of behavior of an emitting dipole in close proximity to nanometal surface by coupling with the image dipole of gold nanomaterials.

Nanoscopic optical rulers beyond the FRET distance limit: fundamentals and applications

In the last few decades, Förster resonance energy transfer (FRET) based spectroscopy rulers have served as a key tool for the understanding of chemical and biochemical processes, even at the single molecule level. Since the FRET process originates from dipole-dipole interactions, the length scale of a FRET ruler is limited to a maximum of 10 nm. Recently, scientists have reported a nanomaterial based long-range optical ruler, where one can overcome the FRET optical ruler distance dependence limit, and which can be very useful for monitoring biological processes that occur across a greater distance than the 10 nm scale. Advancement of nanoscopic long range optical rulers in the last ten years indicate that, in addition to their long-range capability, their brightness, long lifetime, lack of blinking, and chemical stability make nanoparticle based rulers a good choice for long range optical probes. The current review discusses the basic concepts and unique light-focusing properties of plasmonic nanoparticles which are useful in the development of long range one dimensional to three dimensional optical rulers. In addition, to provide the readers with an overview of the exciting opportunities within this field, this review discusses the applications of long range rulers for monitoring biological and chemical processes. At the end, we conclude by speculating on the role of long range optical rulers in future scientific research and discuss possible problems, outlooks and future needs in the use of optical rulers for technological applications.