In vivo biosensing via tissue-localizable near-infrared-fluorescent single-walled carbon nanotubes

Fluorescent Ultrashort Nanotubes from Defect-Induced Chemical Cutting

Ultrashort single-walled carbon nanotubes (SWCNTs) that fluoresce brightly in the shortwave infrared could open exciting opportunities in high-resolution bioimaging and sensing. However, this material remains largely unexplored due to the synthetic challenge. Here, we describe a high-yield synthesis of fluorescent ultrashort nanotubes based on a fundamentally new understanding of defect-induced chemical etching of SWCNTs. We first implant fluorescent sp3 quantum defects along the nanotube sidewalls and then oxidatively cut the nanotubes into ultrashort pieces using hydrogen peroxide. This simple two-step process leads to the synthesis of fluorescent ultrashort nanotubes with a narrow length distribution (38 ± 18 nm) and a yield as high as 57%. Despite their ultrashort length, the cut SWCNTs fluoresce brightly in the shortwave infrared at wavelengths characteristic of the sp3 defects, which provides a spectral fingerprint allowing us to uncover new insights into this defect-induced cutting process. Quantum chemical computations suggest that this etching reaction occurs selectively at the defect sites where hydroxyl radicals (•OH) attack the surrounding electron-rich carbon atoms. This work reveals fundamental insights into defect chemistry and makes fluorescent ultrashort nanotubes synthetically accessible for both basic and applied studies of this largely unexplored but rich class of synthetic molecular nanostructures.

Recent Developments in Nanosensors for Imaging Applications in Biological Systems

Sensors are key tools for monitoring the dynamic changes of biomolecules and biofunctions that encode valuable information that helps us understand underlying biological processes of fundamental importance. Because of their distinctive size-dependent physicochemical properties, materials with nanometer scales have recently emerged as promising candidates for biological sensing applications by offering unique insights into real-time changes of key physiological parameters. This review focuses on recent advances in imaging-based nanosensor developments and applications categorized by their signal transduction mechanisms, namely, fluorescence, plasmonics, MRI, and photoacoustics. We further discuss the synergy created by multimodal nanosensors in which sensor components work based on two or more signal transduction mechanisms.

Nanobiotechnology approaches for engineering smart plant sensors

Nanobiotechnology has the potential to enable smart plant sensors that communicate with and actuate electronic devices for improving plant productivity, optimize and automate water and agrochemical allocation, and enable high-throughput plant chemical phenotyping. Reducing crop loss due to environmental and pathogen-related stresses, improving resource use efficiency and selecting optimal plant traits are major challenges in plant agriculture industries worldwide. New technologies are required to accurately monitor, in real time and with high spatial and temporal resolution, plant physiological and developmental responses to their microenvironment. Nanomaterials are allowing the translation of plant chemical signals into digital information that can be monitored by standoff electronic devices. Herein, we discuss the design and interfacing of smart nanobiotechnology-based sensors that report plant signalling molecules associated with health status to agricultural and phenotyping devices via optical, wireless or electrical signals. We describe how nanomaterial-mediated delivery of genetically encoded sensors can act as tools for research and development of smart plant sensors. We assess performance parameters of smart nanobiotechnology-based sensors in plants (for example, resolution, sensitivity, accuracy and durability) including in vivo optical nanosensors and wearable nanoelectronic sensors. To conclude, we present an integrated and prospective vision on how nanotechnology could enable smart plant sensors that communicate with and actuate electronic devices for monitoring and optimizing individual plant productivity and resource use.

Implantable Nanotube Sensor Platform for Rapid Analyte Detection

The use of nanoparticles within living systems is a growing field, but the long-term effects of introducing nanoparticles to a biological system are unknown. If nanoparticles remain localized after in vivo implantation unanticipated side effects due to unknown biodistribution can be avoided. Unfortunately, stabilization and retention of nanoparticles frequently alters their function.[1] In this work multiple hydrogel platforms are developed to look at long-term localization of nanoparticle sensors with the goal of developing a sensor platform that will stabilize and localize the nanoparticles without altering their function. Two different hydrogel platforms are presented, one with a liquid core of sensors and another with sensors decorating the hydrogel's exterior, that are capable of localizing the nanoparticles without inhibiting their function. With the use of these new hydrogel platforms nanoparticle sensors can be easily implanted in vivo and utilized without concerns of nanoparticle impact on the animal.

A novel "turn-on" mitochondria-targeting near-infrared fluorescent probe for determination and bioimaging cellular hydrogen sulfide

Hydrogen sulfide (H₂S) has been regarded as an important gas transmitter playing vital role in cytoprotective processes and redox signaling. It is very meaningful to monitor and analyze it in biosystem for obtaining important physiological and pathological information. Despite numerous fluorescent probes for cellular H₂S have been reported in past decades, only a few have capability to detect mitochondrial H₂S with near-infrared (NIR) emission. Therefore, a new mitochondria-targeting NIR fluorescent probe (Mito-NSH) for detection of cellular H₂S was developed by introducing 2,4-dinitrophenyl ether into a novel dye (Mito-NOH). A large "turn-on" NIR fluorescence response was obtained due to thiolysis of ether to hydroxyl group when Mito-NSH was treated with NaHS. Moreover, Mito-NSH could quantitatively detect H₂S at concentration ranging from 0 to 30 μM with a detection limit of 68.2 nM, and it exerts some superior optical properties, such as large stokes shift (107 nm), highly selectively mitochondria location, fast response and high selectivity to H₂S. More impressively, it was successfully applied to imaging exogenous and endogenously generated H₂S in living HeLa cells via confocal fluorescence microscopy.

A Novel Ruthenium-based Molecular Sensor to Detect Endothelial Nitric Oxide

Nitric oxide (NO) is a key regulator of endothelial cell and vascular function. The direct measurement of NO is challenging due to its short half-life, and as such surrogate measurements are typically used to approximate its relative concentrations. Here we demonstrate that ruthenium-based [Ru(bpy)₂(dabpy)]²⁺ is a potent sensor for NO in its irreversible, NO-bound active form, [Ru(bpy)₂(T-bpy)]²⁺. Using spectrophotometry we established the sensor’s ability to detect and measure soluble NO in a concentration-dependent manner in cell-free media. Endothelial cells cultured with acetylcholine or hydrogen peroxide to induce endogenous NO production showed modest increases of 7.3 ± 7.1% and 36.3 ± 25.0% respectively in fluorescence signal from baseline state, while addition of exogenous NO increased their fluorescence by 5.2-fold. The changes in fluorescence signal were proportionate and comparable against conventional NO assays. Rabbit blood samples immediately exposed to [Ru(bpy)₂(dabpy)]²⁺ displayed 8-fold higher mean fluorescence, relative to blood without sensor. Approximately 14% of the observed signal was NO/NO adduct-specific. Optimal readings were obtained when sensor was added to freshly collected blood, remaining stable during subsequent freeze-thaw cycles. Clinical studies are now required to test the utility of [Ru(bpy)₂(dabpy)]²⁺ as a sensor to detect changes in NO from human blood samples in cardiovascular health and disease.

Multiwalled carbon nanotube-based nanosensor for ultrasensitive detection of uric acid, dopamine, and ascorbic acid

A novel multiwalled carbon nanotube (MWCNT) based sensor was fabricated as a highly precise and stable electrochemical sensor. The synthesized sensor which consists of ZnNi bimetallic nanoalloy called the ZnNi NPs@f-MWCNT sensor, have been used for the simultaneous detection of uric acid (UA), dopamine (DA) and ascorbic acid (AA). The ZnNi NPs@f-MWCNT sensor obtained based on the microwave irradiation process, and its characterization was performed by using several physical techniques such as XRD, XPS, TEM, Raman, etc. The characterization showed that this sensor has excellent properties such as rich pore channels, excellent structural durability, and large surface area. These properties facilitated mass transfer and electron conductions. It was observed that the obtained sensor gave high electrochemical activity and wide linear responses (0.3-1.1 mM AA, 0.2-1.2 mM DA, 0.2-1.1 mM UA) in the detection of uric acid (UA), dopamine (DA) and ascorbic acid (AA). In addition to these properties, it has been found that the sensor has excellent anti-interferents properties towards AlCl₃, KCl₃, glucose, etc. and ZnNi NPs@f-MWCNT sensor was further applied to determine uric acid (UA), dopamine (DA) and ascorbic acid (AA) in real samples.

Implanted Nanosensors in Marine Organisms for Physiological Biologging: Design, Feasibility, and Species Variability

In recent decades, biologists have sought to tag animals with various sensors to study aspects of their behavior otherwise inaccessible from controlled laboratory experiments. Despite this, chemical information, both environmental and physiological, remains challenging to collect despite its tremendous potential to elucidate a wide range of animal behaviors. In this work, we explore the design, feasibility, and data collection constraints of implantable, near-infrared fluorescent nanosensors based on DNA-wrapped single-wall carbon nanotubes (SWNT) embedded within a biocompatible poly(ethylene glycol) diacrylate (PEGDA) hydrogel. These sensors are enabled by Corona Phase Molecular Recognition (CoPhMoRe) to provide selective chemical detection for marine organism biologging. Riboflavin, a key nutrient in oxidative phosphorylation, is utilized as a model analyte in in vitro and ex vivo tissue measurements. Nine species of bony fish, sharks, eels, and turtles were utilized on site at Oceanogràfic in Valencia, Spain to investigate sensor design parameters, including implantation depth, sensor imaging and detection limits, fluence, and stability, as well as acute and long-term biocompatibility. Hydrogels were implanted subcutaneously and imaged using a customized, field-portable Raspberry Pi camera system. Hydrogels could be detected up to depths of 7 mm in the skin and muscle tissue of deceased teleost fish ( Sparus aurata and Stenotomus chrysops) and a deceased catshark ( Galeus melastomus). The effects of tissue heterogeneity on hydrogel delivery and fluorescence visibility were explored, with darker tissues masking hydrogel fluorescence. Hydrogels were implanted into a living eastern river cooter ( Pseudemys concinna), a European eel ( Anguilla anguilla), and a second species of catshark ( Scyliorhinus stellaris). The animals displayed no observable changes in movement and feeding patterns. Imaging by high-resolution ultrasound indicated no changes in tissue structure in the eel and catshark. In the turtle, some tissue reaction was detected upon dissection and histopathology. Analysis of movement patterns in sarasa comet goldfish ( Carassius auratus) indicated that the hydrogel implants did not affect swimming patterns. Taken together, these results indicate that this implantable form factor is a promising technique for biologging using aquatic vertebrates with further development. Future work will tune the sensor detection range to the physiological range of riboflavin, develop strategies to normalize sensor signal to account for the optical heterogeneity of animal tissues, and design a flexible, wearable device incorporating optoelectronic components that will enable sensor measurements in moving animals. This work advances the application of nanosensors to organisms beyond the commonly used rodent and zebrafish models and is an important step toward the physiological biologging of aquatic organisms.

Delayed Increase in Near-Infrared Fluorescence in Cultured Murine Cancer Cells Labeled with Oxygen-Doped Single-Walled Carbon Nanotubes

The labeling technique for cells with over-thousand-nanometer near-infrared (OTN-NIR) fluorescent probes has attracted much attention for in vivo deep imaging for cell tracking and cancer metastasis, because of low scattering and absorption of OTN-NIR light by biological tissues. However, the intracellular behavior following the uptake of the single-walled carbon nanotubes (SWCNTs), an OTN-NIR fluorophore, remains unknown. The aim of this study is to investigate the time-dependent change in OTN-NIR fluorescence images of cultured murine cancer cells (Colon-26) following treatment with a recently developed OTN-NIR fluorescent probe, epoxide-type oxygen-doped SWCNTs (o-SWCNTs). The o-SWCNTs were synthesized by oxygenation of SWCNTs by ozone under ultraviolet irradiation and were dispersed in an aqueous solution of N-(carbonyl-methoxypolyethyleneglycol 2000)-1,2-distearoyl- sn-glycero-3-phosphoethanolamine to prepare biocompatible o-SWCNTs (o-SWCNT-PEG). OTN-NIR fluorescent o-SWCNT-PEG showed an abnormal behavior following cellular uptake. OTN-NIR fluorescence was not observed in the cells after 24 h incubation with the o-SWCNT-PEG, but clearly increased with longer incubation time from three days after the treatment. This result was further confirmed by Raman microscopy, suggesting that OTN-NIR fluorescence intensity was associated with the cellular uptake of the o-SWCNT-PEG. These results suggest that the Colon-26 cells were successfully labeled by the o-SWCNT-PEG that emit OTN-NIR fluorescence. The o-SWCNT-PEG may aggregate in the cells over time, which could favor their internalization. This delayed concentration followed by a long retention of the o-SWCNT-PEG in cells will facilitate further biotechnological applications of the o-SWCNTs to in vivo deep OTN-NIR fluorescent imaging.

Chemometric Approaches for Developing Infrared Nanosensors To Image Anthracyclines

Generation, identification, and validation of optical probes to image molecular targets in a biological milieu remain a challenge. Synthetic molecular recognition approaches leveraging the intrinsic near-infrared fluorescence of single-walled carbon nanotubes are promising for long-term biochemical imaging in tissues. However, generation of nanosensors for selective imaging of molecular targets requires a heuristic approach. Here, we present a chemometric platform for rapidly screening libraries of candidate single-walled carbon nanotube nanosensors against biochemical analytes to quantify the fluorescence response to small molecules, including vitamins, neurotransmitters, and chemotherapeutics. We further show this method can be applied to identify biochemical analytes that selectively modulate the intrinsic near-infrared fluorescence of candidate nanosensors. Chemometric analysis thus enables identification of nanosensor-analyte "hits" and also nanosensor fluorescence signaling modalities such as wavelength shifts that are optimal for translation to biological imaging. Through this approach, we identify and characterize a nanosensor for the chemotherapeutic anthracycline doxorubicin (DOX), which provides a ≤17 nm fluorescence red-shift and exhibits an 8 μM limit of detection, compatible with peak circulatory concentrations of doxorubicin common in therapeutic administration. We demonstrate the selectivity of this nanosensor over dacarbazine, a chemotherapeutic commonly co-injected with doxorubicin. Lastly, we establish nanosensor tissue compatibility for imaging of doxorubicin in muscle tissue by incorporating nanosensors into the mouse hindlimb and measuring the nanosensor response to exogenous DOX administration. Our results motivate chemometric approaches to nanosensor discovery for chronic imaging of drug partitioning into tissues and toward real-time monitoring of drug accumulation.

Phenylboronic acid derivative-modified (6,5) single-wall carbon nanotube probes for detecting glucose and hydrogen peroxide

In this paper, we presented a new method for constructing near-infrared fluorescence probes and their applications in detecting glucose and hydrogen peroxide (H₂O₂).

Organic Semiconducting Agents for Deep-Tissue Molecular Imaging: Second Near-Infrared Fluorescence, Self-Luminescence, and Photoacoustics

Optical imaging has played a pivotal role in biology and medicine, but it faces challenges of relatively low tissue penetration and poor signal-to-background ratio due to light scattering and tissue autofluorescence. To overcome these issues, second near-infrared fluorescence, self-luminescence, and photoacoustic imaging have recently emerged, which utilize an optical region with reduced light-tissue interactions, eliminate real-time light excitation, and detect acoustic signals with negligible attenuation, respectively. Because there are only a few endogenous molecules absorbing or emitting above the visible region, development of contrast agents is essential for those deep-tissue optical imaging modalities. Organic semiconducting agents with π-conjugated frameworks can be synthesized to meet different optical imaging requirements due to their easy chemical modification and legible structure-property relation. Herein, the deep-tissue optical imaging applications of organic semiconducting agents including small-molecule agents and nanoparticle derivatives are summarized. In particular, the molecular engineering and nanoformulation approaches to further improve the tissue penetration and detection sensitivity of these optical imaging modalities are highlighted. Finally, current challenges and potential opportunities in this emerging subfield of biomedical imaging are discussed.

Hypoxia-triggered single molecule probe for high-contrast NIR II/PA tumor imaging and robust photothermal therapy

Hypoxia is a common characteristic of solid tumors. This important feature is associated with resistance to radio-chemotherapy, which results in poor prognosis and probability of tumor recurrence. Taking advantage of background-free NIR II fluorescence imaging and deeper-penetrating photoacoustic (PA) imaging, we developed a hypoxia-triggered and nitroreductase (NTR) enzyme-responsive single molecule probe for high-contrast NIR II/PA tumor imaging and hypoxia-activated photothermal therapy (PTT), which will overcome cellular resistance during hypoxia. Methods: The single molecule probe IR1048-MZ was synthesized by conjugating a nitro imidazole group as a specific hypoxia trigger with an IR-1048 dye as a NIR II/PA signal reporter. We investigated the NIR II fluorescence, NIR absorbance and photothermal effect in different hypoxia conditions in vitro, and performed NIR II/PA tumor imaging and hypoxia-activated photothermal therapy in mice. Results: This versatile molecular probe IR1048-MZ not only realized high-contrast tumor visualization with a clear boundary by NIR II fluorescence imaging, but also afforded deep-tissue penetration at the centimeter level by 3D PA imaging. Moreover, after being activated by NTR that is overexpressed in hypoxic tumors, the probe exhibited a significant photothermal effect for curative tumor ablation with no recurrence. Conclusions: We have developed the first hypoxia-triggered and NTR enzyme-responsive single molecule probe for high-contrast NIR II/PA tumor imaging and hypoxia-activated photothermal therapy. By tracing the activity of NTR, IR1048-MZ may be a promising contrast agent and theranostic formulation for other hypoxia-related diseases (such as cancer, inflammation, stroke, and cardiac ischemia).

Challenges and Opportunities for Intravital Near-Infrared Fluorescence Imaging Technology in the Second Transparency Window

The past decade has witnessed rapid technological development on nanoscale probes and imaging optics in the second near-infrared transparency window (NIR-II, 1000-1700 nm). These methods hold great promise for biomedical applications due to their deep penetration through tissues and high fidelity of images. However, applications of these techniques in biomedical research and translational medicine will require a number of issues to be addressed. In this Perspective, we examine the technical challenges for intravital NIR-II fluorescence imaging technology and discuss where the development of this cutting-edge technique fits in the future.

A Fluorescent Carbon Nanotube Sensor Detects the Metastatic Prostate Cancer Biomarker uPA

Therapeutic outcomes in patients with prostate cancer are hindered by the inability to discern indolent versus aggressive disease. To address this problem, we developed a quantitative fluorescent nanosensor for the cancer biomarker urokinase plasminogen activator (uPA). We used the unique fluorescent characteristics of single-walled carbon nanotubes (SWCNT) to engineer an optical sensor that responds to uPA via optical bandgap modulation in complex protein environments. The sensing characteristics of this construct were modulated by passivation of the hydrophobic SWCNT surface with bovine serum albumin (BSA). The sensor enabled quantitative detection of known uPA concentrations in human blood products. These experiments potentiate future use of this technology as a rapid, point-of-care sensor for biomarker measurements in patient fluid samples. We expect that further work will develop a method to discern aggressive vs indolent prostate cancer and reduce overtreatment of this disease.

Investigating supramolecular systems using Förster resonance energy transfer

Supramolecular systems have applications in areas as diverse as materials science, biochemistry, analytical chemistry, and nanomedicine. However, analyzing such systems can be challenging due to the wide range of time scales, binding strengths, distances, and concentrations at which non-covalent phenomena take place. Due to their versatility and sensitivity, Förster resonance energy transfer (FRET)-based techniques are excellently suited to meet such challenges. Here, we detail the ways in which FRET has been used to study non-covalent interactions in both synthetic and biological supramolecular systems. Among other topics, we examine methods to measure molecular forces, determine protein conformations, monitor assembly kinetics, and visualize in vivo drug release from nanoparticles. Furthermore, we highlight multiplex FRET techniques, discuss the field's limitations, and provide a perspective on new developments.

Carbon Nanomaterials in Optical Detection

Owing to their unique optical, electronic, mechanical, and chemical properties, flexible chemical modification, large surface coverage and ready cellular uptake, various carbon nanomaterials such as carbon nanotubes (CNTs), graphene and its derivatives, carbon dots (CDs), graphene quantum dots, fullerenes, carbon nanohorns (CNHs) and carbon nano-onions (CNOs), have been widely explored for use in optical detection. Most of them are based on fluorescence changes. In this chapter, we will focus on carbon nanomaterials-based optical detection applications, mainly including fluorescence sensing and bio-imaging. Moreover, perspectives on future exploration of carbon nanomaterials for optical detection are also given.

Light induced DNA-functionalized TiO2 nanocrystalline interface: Theoretical and experimental insights towards DNA damage detection

Owing to the emerging applications of DNA-functionalized TiO₂ nanocrystals towards DNA damage detection, it is inevitable to understand the better chemistry as well as in-depth molecular interaction phenomena. Fundamentally, energy difference underlies the layer-by-layer construction, resulted in the increase of the interaction energy and thus, altering the electrochemical behavior. Herein, Density functional theory (DFT) calculations were performed using DMol3 and DFTB+ codes successfully to elucidate the structural, electronics, and vibrational properties of the layer-by-layer components composing ss-DNA/dopamine/TiO₂/FTO. The obtained results are in good agreement with the experimental findings. The band gaps of FTO and TiO₂ were computationally obtained at 3.335 and 3.136 eV which are comparable with the experimental data (3.500 eV; FTO and 3.200 eV; TiO₂). Frontier orbital analysis is also considered to elucidate their electron transfer phenomena. Further, a 100 ns MD simulations are carried out using canonical ensemble embedded with COMPASS-Universal Forcefields generating useful thermodynamics parameters. Binding energies indicate increasing interaction energies for the layer-by-layer nanosystem, in agreement with the increasing diameter of electrochemical impedance spectroscopy (EIS) semicircle. Our results reveal the fundamental understanding of the DNA-functionalized TiO₂ nanocrystals down to molecular and electronic level and further, paving a way of its application towards nanoelectrochemical DNA biosensors.

Recent Advances in the Therapeutic and Diagnostic Use of Liposomes and Carbon Nanomaterials in Ischemic Stroke

The complexity of the central nervous system (CNS), its limited self-repairing capacity and the ineffective delivery of most CNS drugs to the brain contribute to the irreversible and progressive nature of many neurological diseases and also the severity of the outcome. Therefore, neurological disorders belong to the group of pathologies with the greatest need of new technologies for diagnostics and therapeutics. In this scenario, nanotechnology has emerged with innovative and promising biomaterials and tools. This review focuses on ischemic stroke, being one of the major causes of death and serious long-term disabilities worldwide, and the recent advances in the study of liposomes and carbon nanomaterials for therapeutic and diagnostic purposes. Ischemic stroke occurs when blood flow to the brain is insufficient to meet metabolic demand, leading to a cascade of physiopathological events in the CNS including local blood brain barrier (BBB) disruption. However, to date, the only treatment approved by the FDA for this pathology is based on the potentially toxic tissue plasminogen activator. The techniques currently available for diagnosis of stroke also lack sensitivity. Liposomes and carbon nanomaterials were selected for comparison in this review, because of their very distinct characteristics and ranges of applications. Liposomes represent a biomimetic system, with composition, structural organization and properties very similar to biological membranes. On the other hand, carbon nanomaterials, which are not naturally encountered in the human body, exhibit new modes of interaction with biological molecules and systems, resulting in unique pharmacological properties. In the last years, several neuroprotective agents have been evaluated under the encapsulated form in liposomes, in experimental models of stroke. Effective drug delivery to the brain and neuroprotection were achieved using stealth liposomes bearing targeting ligands onto their surface for brain endothelial cells and ischemic tissues receptors. Carbon nanomaterials including nanotubes, fullerenes and graphene, started to be investigated and potential applications for therapy, biosensing and imaging have been identified based on their antioxidant action, their intrinsic photoluminescence, their ability to cross the BBB, transitorily decrease the BBB paracellular tightness, carry oligonucleotides and cells and induce cell differentiation. The potential future developments in the field are finally discussed.

Covalent functionalization of SWCNT with combretastatin A4 for cancer therapy

Single walled carbon nanotubes (SWCNT) are currently under intensive investigation by many labs all over the world for being promising candidates for cancer chemotherapy delivery. On the other hand, combretastatin A4 (CA4) is an anticancer drug that induces cell apoptosis by inhibiting tubulin polymerization. However, it has the disadvantage of low water solubility and the non-selective targeting. Therefore, we aim to create nano-drug from the functionalization of SWCNT covalently with CA4 through click reaction in the presence of tetraethylene glycol linker in order to improve its dispersibility. Scanning electron microscopy and transmission electron microscopy showed good dispersibility of the functionalized SWCNT with diameters of 5-15 nm. Moreover, thermogravometric analysis showed that the efficiency of SWCNT functionalization was around 45%. The in vitro release profile of CA4 at physiological conditions showed that approximately 90% of the loaded drug was released over 50 h. After that MTS test was used to determine the suitable concentration range for the in vitro investigation of the SWCNT-CA4. After that the cytotoxic activity of the SWCNT-CA4 was evaluated by flow cytometry using annexin V/propidium iodide (PI) test. In comparison with free CA4, SWCNT-CA4 treatment demonstrated a significant increase in necrotic cells (around 50%) at the expense of the proportion of the apoptotic cells. Moreover, cell cycle PI test demonstrated that free CA4 and SWCNT-CA4 caused G2/M arrest. However with CA4 treatment higher proportion of cells were in the S-phase while with SWCNT-CA4 treatment greater proportion of cells appeared to be in the G1-phase. Taken together, the provided data suggest that the novel SWCNT-CA4 has a significant anticancer activity that might be superior to that of free CA4.

In Vivo and In Situ Detection of Macromolecular Free Radicals Using Immuno-Spin Trapping and Molecular Magnetic Resonance Imaging

SIGNIFICANCE

In vivo free radical imaging in preclinical models of disease has become a reality. Free radicals have traditionally been characterized by electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy coupled with spin trapping. The disadvantage of the ESR/EPR approach is that spin adducts are short-lived due to biological reductive and/or oxidative processes. Immuno-spin trapping (IST) involves the use of an antibody that recognizes macromolecular 5,5-dimethyl-pyrroline-N-oxide (DMPO) spin adducts (anti-DMPO antibody), regardless of the oxidative/reductive state of trapped radical adducts. Recent Advances: The IST approach has been extended to an in vivo application that combines IST with molecular magnetic resonance imaging (mMRI). This combined IST-mMRI approach involves the use of a spin-trapping agent, DMPO, to trap free radicals in disease models, and administration of an mMRI probe, an anti-DMPO probe, which combines an antibody against DMPO-radical adducts and an MRI contrast agent, resulting in targeted free radical adduct detection.

CRITICAL ISSUES

The combined IST-mMRI approach has been used in several rodent disease models, including diabetes, amyotrophic lateral sclerosis (ALS), gliomas, and septic encephalopathy. The advantage of this approach is that heterogeneous levels of trapped free radicals can be detected directly in vivo and in situ to pin point where free radicals are formed in different tissues.

FUTURE DIRECTIONS

The approach can also be used to assess therapeutic agents that are either free radical scavengers or generate free radicals. Smaller probe constructs and radical identification approaches are being considered. The focus of this review is on the different applications that have been studied, advantages and limitations, and future directions. Antioxid. Redox Signal. 28, 1404-1415.

Recent advances in electrochemical non-enzymatic glucose sensors - A review

This review encompasses the mechanisms of electrochemical glucose detection and recent advances in non-enzymatic glucose sensors based on a variety of materials ranging from platinum, gold, metal alloys/adatom, non-precious transition metal/metal oxides to glucose-specific organic materials. It shows that the discovery of new materials based on unique nanostructures have not only provided the detailed insight into non-enzymatic glucose oxidation, but also demonstrated the possibility of direct detection in whole blood or interstitial fluids. We critically evaluate various aspects of non-enzymatic electrochemical glucose sensors in terms of significance as well as performance. Beyond laboratory tests, the prospect of commercialization of non-enzymatic glucose sensors is discussed.

Role of Au(NPs) in the enhanced response of Au(NPs)-decorated MWCNT electrochemical biosensor

Background

The combination of Au-metallic-NPs and CNTs are a new class of hybrid nanomaterials for the development of electrochemical biosensor. Concentration of Au(nanoparticles [NPs]) in the electrochemical biosensor is crucial for the efficient charge transfer between the Au-NPs-MWCNTs modified electrode and electrolytic solution.

Methods

In this work, the charge transfer kinetics in the glassy carbon electrode (GCE) modified with Au(NPs)–multiwalled carbon nanotube (MWCNT) nanohybrid with varied concentrations of Au(NPs) in the range 40–100 nM was studied using electrochemical impedance spectroscopy (EIS). Field emission scanning electron microscopy and transmission electron microscopy confirmed the attachment of Au(NPs) on the surface of MWCNTs.

Results

The cyclic voltammetry and EIS results showed that the charge transfer mechanism was diffusion controlled and the rate of charge transfer was dependent on the concentration of Au(NPs) in the nanohybrid. The formation of spherical diffusion zone, which was dependent on the concentration of Au(NPs) in nanohybrids, was attributed to result in 3 times the increase in the charge transfer rate k_s, 5 times increase in mass transfer, and 5% (9%) increase in I_pa (I_pc) observed in cyclic voltammetry in 80 nM Au(NP) nanohybrid-modified GCE from MWCNT-modified GCE. The work was extended to probe the effect of charge transfer rates at various concentrations of Au(NPs) in the nanohybrid-modified electrodes in the presence of Escherichia coli. The cyclic voltammetry results clearly showed the best results for 80 nM Au(NPs) in nanohybrid electrode.

Conclusion

The present study suggested that the formation of spherical diffusion zone in nanohybrid-modified electrodes is critical for the enhanced electrochemical biosensing applications.

Noninvasive ovarian cancer biomarker detection via an optical nanosensor implant

Patients with high-grade serous ovarian carcinoma (HGSC) exhibit poor 5-year survival rates, which may be significantly improved by early-stage detection. The U.S. Food and Drug Administration-approved biomarkers for HGSC-CA-125 (cancer antigen 125) and HE4 (human epididymis protein 4)-do not generally appear at detectable levels in the serum until advanced stages of the disease. An implantable device placed proximal to disease sites, such as in or near the fallopian tube, ovary, uterine cavity, or peritoneal cavity, may constitute a feasible strategy to improve detection of HGSC. We engineered a prototype optical sensor composed of an antibody-functionalized carbon nanotube complex, which responds quantitatively to HE4 via modulation of the nanotube optical bandgap. The complexes measured HE4 with nanomolar sensitivity to differentiate disease from benign patient biofluids. The sensors were implanted into four models of ovarian cancer, within a semipermeable membrane, enabling the optical detection of HE4 within the live animals. We present the first in vivo optical nanosensor capable of noninvasive cancer biomarker detection in orthotopic models of disease.

Insulin Detection Using a Corona Phase Molecular Recognition Site on Single-Walled Carbon Nanotubes

Corona phase molecular recognition (CoPhMoRe) is a technique whereby an external, adsorbed phase around a colloidal nanoparticle is selected such that its molecular conformation or interaction recognizes a specific target analyte. In this work, we employ a high-throughput screening of a library of poly(ethylene glycol) (PEG)-conjugated lipids adsorbed onto near-infrared fluorescent single-walled carbon nanotubes to discover a corona phase selective for insulin. We find that a C₁₆-PEG(2000 Da)-ceramide causes a 62% fluorescent intensity decrease of the (10,2) chirality nanotube in the presence of 20 μg/mL insulin. The insulin protein has no prior affinity toward the C₁₆-PEG(2000 Da)-ceramide molecules in free solution, verified by isothermal titration calorimetry, and the interaction occurs only upon their adsorption onto the single-walled carbon nanotube scaffolds. Testing a panel of proteins originating from human blood as well as short 7 amino acid fragments of the insulin peptide rules out nonselective recognition mechanisms such as molecular weight, isoelectric point, and hydrophobicity-based detection. Interestingly, longer fragments of isolated α- and β-peptide chains of insulin are detected by the construct, albeit with lower affinity compared to that of the intact insulin protein, suggesting that the construct recognizes insulin in its native form and conformation. Finally, the insulin recognition and the quantification of its solution concentration were demonstrated both in buffer and in blood serum, showing that the CoPhMoRe construct works in this complex environment despite the presence of potential nonspecific adsorption. Our results further motivate the search for nonbiological synthetic recognition sites and open up a new path for continuous insulin monitoring in vivo with the hope of improving glycemic control in closed-loop artificial pancreas systems.

High-efficiency X-ray luminescence in Eu3+-activated tungstate nanoprobes for optical imaging through energy transfer sensitization

X-ray luminescence optical imaging has been recognized as a powerful technique for medical diagnosis due to its deep penetration and low auto-fluorescence in tissues. However, the low luminescence efficiency of current X-ray luminescence nanoprobes remains a major hurdle for sensitive bioimaging in practical medical applications. Here we present a new kind of energy transfer-sensitized X-ray luminescence nanoprobe (PEG-NaGd(WO₄)₂:Eu) for highly effective optical bioimaging. Under X-ray excitation, the tungstate host absorbs the X-ray photons and then transfers the energy to the Eu³⁺ luminescence center, thus enhancing the luminescence efficiency of the nanoprobes for high sensitivity optical in vivo imaging. Moreover, the shortened T₁ relaxation response of Gd³⁺ ions and X-ray attenuation capability of W atoms enable the nanoprobes to serve as efficient contrast agents for magnetic resonance imaging (MRI) and computed tomography (CT) imaging. Therefore, combined with the MRI, CT and X-ray luminescence imaging capabilities, the present PEG-NaGd(WO₄)₂:Eu nanoprobes could be used as promising multimodal imaging contrast agents in biological systems.

Optical conductivity-based ultrasensitive mid-infrared biosensing on a hybrid metasurface

Optical devices are highly attractive for biosensing as they can not only enable quantitative measurements of analytes but also provide information on molecular structures. Unfortunately, typical refractive index-based optical sensors do not have sufficient sensitivity to probe the binding of low-molecular-weight analytes. Non-optical devices such as field-effect transistors can be more sensitive but do not offer some of the significant features of optical devices, particularly molecular fingerprinting. We present optical conductivity-based mid-infrared (mid-IR) biosensors that allow for sensitive and quantitative measurements of low-molecular-weight analytes as well as the enhancement of spectral fingerprints. The sensors employ a hybrid metasurface consisting of monolayer graphene and metallic nano-antennas and combine individual advantages of plasmonic, electronic and spectroscopic approaches. First, the hybrid metasurface sensors can optically detect target molecule-induced carrier doping to graphene, allowing highly sensitive detection of low-molecular-weight analytes despite their small sizes. Second, the resonance shifts caused by changes in graphene optical conductivity is a well-defined function of graphene carrier density, thereby allowing for quantification of the binding of molecules. Third, the sensor performance is highly stable and consistent thanks to its insensitivity to graphene carrier mobility degradation. Finally, the sensors can also act as substrates for surface-enhanced infrared spectroscopy. We demonstrated the measurement of monolayers of sub-nanometer-sized molecules or particles and affinity binding-based quantitative detection of glucose down to 200 pM (36 pg/mL). We also demonstrated enhanced fingerprinting of minute quantities of glucose and polymer molecules.

Crucial breakthrough of second near-infrared biological window fluorophores: design and synthesis toward multimodal imaging and theranostics

Recent advances in the chemical design and synthesis of fluorophores in the second near-infrared biological window (NIR-II) for multimodal imaging and theranostics are summarized and highlighted in this review article.

Self-Powered Implantable Skin-Like Glucometer for Real-Time Detection of Blood Glucose Level In Vivo

Implantable bioelectronics for analyzing physiological biomarkers has recently been recognized as a promising technique in medical treatment or diagnostics. In this study, we developed a self-powered implantable skin-like glucometer for real-time detection of blood glucose level in vivo. Based on the piezo-enzymatic-reaction coupling effect of GOx@ZnO nanowire, the device under an applied deformation can actively output piezoelectric signal containing the glucose-detecting information. No external electricity power source or battery is needed for this device, and the outputting piezoelectric voltage acts as both the biosensing signal and electricity power. A practical application of the skin-like glucometer implanted in mouse body for detecting blood glucose level has been simply demonstrated. These results provide a new technique path for diabetes prophylaxis and treatment.

Quantum yield in polymer wrapped single walled carbon nanotubes: a computational model

Quantum yield in polymer wrapped single walled carbon nanotubes (SWCNTs) has been computationally investigated using a 2D model of exciton decay with non-radiative channels due to the diffusive motion across the nanotube surface. Beside the role of SWCNT's ends as the exciton quenchers, we have considered the influence of the wrapping polymer through its chemistry and wrapping angle. The model has been solved exactly for zero-angle wrapping, a particular case when the polymer interfaces the nanotube along its axis. The general case has been treated numerically and it has been concluded that the wrapping angle has no relevant influence upon the quantum yield values which are of experimental interest. A wide range of quantum yield values computed in the present contribution can be helpful in understanding potentially available photoluminescence data of SWCNTs wrapped with a variety of polymer families.

Control of Carbon Nanotube Solvatochromic Response to Chemotherapeutic Agents

Alkylating agents such as cisplatin play an essential role in chemotherapy regimens, but initial and acquired resistance in many cancer types often dampen therapeutic response. The poor understanding of the mechanisms of resistance highlight the need for quantitative measurements of alkylating agent distribution at both the tissue and subcellular levels. Sensors for use in live animals and cells would allow for more effective study of drug action and resistance. Toward this end, single-walled carbon nanotubes suspended with single-stranded DNA have suitable optical properties for in vivo sensors, such as near-infrared emission and sensitivity to the local environment via solvatochromic responses. Currently, solvatochromic changes of such sensors have been limited by the chemical nature of the analyte, making it impossible to control the direction of energy emission changes. Here, we describe a new approach to control the direction and magnitude of solvatochromic responses of carbon nanotubes. We found that the alkylation of DNA on the nanotube surface can result in small changes in DNA conformation that allow the adsorption of amphiphiles to produce large differences (>14 nm) in response to different drugs. The technique surprisingly revealed differences among drugs upon alkylation. The ability to control carbon nanotube solvatochromism as desired may potentially expand the application of nanotube-based optical sensors for new classes of analytes.

A Self-Powered Wearable Noninvasive Electronic-Skin for Perspiration Analysis Based on Piezo-Biosensing Unit Matrix of Enzyme/ZnO Nanoarrays

The emerging multifunctional flexible electronic-skin for establishing body-electric interaction can enable real-time monitoring of personal health status as a new personalized medicine technique. A key difficulty in the device design is the flexible power supply. Here a self-powered wearable noninvasive electronic-skin for perspiration analysis has been realized on the basis of a piezo-biosensing unit matrix of enzyme/ZnO nanoarrays. The electronic-skin can detect lactate, glucose, uric acid, and urea in the perspiration, and no outside electrical power supply or battery is used in the biosensing process. The piezoelectric impulse of the piezo-biosensing units serves as the power supply and the data biosensor. The working mechanism can be ascribed to the piezoelectric-enzymatic-reaction coupling effect of enzyme/ZnO nanowires. The electronic-skin can real-time/continuously monitor the physiological state of a runner through analyzing the perspiration on his skin. This approach can promote the development of a new-type of body electric and self-powered biosensing electronic-skin.

A Reactive Oxygen/Nitrogen Species Sensor Fabricated from an Electrode Modified with a Polymerized Iron Porphyrin and a Polymer Electrolyte Membrane

We have developed an electrochemical reactive oxygen/nitrogen species sensor that can detect superoxide anion radicals (O₂^-•) and nitric oxide (NO). The reactive oxygen/nitrogen species sensor was fabricated by surface modification of an electrode with polymerized iron tetrakis(3-thienyl)porphyrin (FeT3ThP), and it can detect either O₂^-• or NO by switching the applied potential. Furthermore, we fabricated a sensor with improved selectivity by coating a Nafion^® film onto the poly(FeT3ThP)-modified electrode. An interference current caused by NO₂^- was seen for the poly(FeT3ThP)-modified electrode, while the interference current was significantly reduced at the Nafion^®/poly(FeT3ThP)-modified electrode, leading to improved selectivity for NO detection. The current response at the Nafion^®/poly(FeT3ThP)-modified electrode exhibited good linearity in the O₂^-• and NO concentration ranges 1.3 - 4.1, and 0.5 - 10 μM, respectively. The Nafion^®/poly(FeT3ThP)-modified and poly(FeT3ThP)-modified electrodes are highly versatile, because these electrodes can detect either O₂^-• or NO by switching the applied potential. Since the Nafion^®/poly(FeT3ThP)-modified and poly(FeT3ThP)-modified electrodes contain no bio-derived compounds, the reactive oxygen/nitrogen species sensor should be safe even when it is used in vivo.

A hydrogen peroxide sensor based on TNM functionalized reduced graphene oxide grafted with highly monodisperse Pd nanoparticles

Addressed herein, we report the synthesis and characterization of a tert-nonyl mercaptan (TNM) functionalized reduced graphene oxide (rGO) supported palladium (Pd) nanoparticles (NPs) (Pd/TNM@rGO) as electrochemical sensor. The highly monodisperse Pd/TNM@rGO nanocomposite was applied for electrochemical determination of hydrogen peroxide (H₂O₂) at a potential range of -0.6 to +0.8 V. The Pd/TNM@rGO sensor demonstrated very high activity, sensitivity, reusability and durability toward H₂O₂ sensing. The well dispersed Pd/TNM@rGO nanocomposite has been characterized by using several analytical techniques such as, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and electrochemical impedance spectroscopy (EIS). The catalytic performance of prepared biosensor was also characterized by using cyclic voltammetry (CV) and chronoamperometry (CA) methods. The proposed H₂O₂ biosensor showed a broad linear range up to 12 mM, and a very low detection limit of 0.0025 μM, with a quick response time of less than 10 s. Additionally, the biosensor exhibited great capability, reproducibility and durability for the examination of H₂O₂.

Emerging Trends in Micro- and Nanoscale Technologies in Medicine: From Basic Discoveries to Translation

We discuss the state of the art and innovative micro- and nanoscale technologies that are finding niches and opening up new opportunities in medicine, particularly in diagnostic and therapeutic applications. We take the design of point-of-care applications and the capture of circulating tumor cells as illustrative examples of the integration of micro- and nanotechnologies into solutions of diagnostic challenges. We describe several novel nanotechnologies that enable imaging cellular structures and molecular events. In therapeutics, we describe the utilization of micro- and nanotechnologies in applications including drug delivery, tissue engineering, and pharmaceutical development/testing. In addition, we discuss relevant challenges that micro- and nanotechnologies face in achieving cost-effective and widespread clinical implementation as well as forecasted applications of micro- and nanotechnologies in medicine.

A high quantum yield molecule-protein complex fluorophore for near-infrared II imaging

Fluorescence imaging in the second near-infrared window (NIR-II) allows visualization of deep anatomical features with an unprecedented degree of clarity. NIR-II fluorophores draw from a broad spectrum of materials spanning semiconducting nanomaterials to organic molecular dyes, yet unfortunately all water-soluble organic molecules with >1,000 nm emission suffer from low quantum yields that have limited temporal resolution and penetration depth. Here, we report tailoring the supramolecular assemblies of protein complexes with a sulfonated NIR-II organic dye (CH-4T) to produce a brilliant 110-fold increase in fluorescence, resulting in the highest quantum yield molecular fluorophore thus far. The bright molecular complex allowed for the fastest video-rate imaging in the second NIR window with ∼50-fold reduced exposure times at a fast 50 frames-per-second (FPS) capable of resolving mouse cardiac cycles. In addition, we demonstrate that the NIR-II molecular complexes are superior to clinically approved ICG for lymph node imaging deep within the mouse body.

Near-infrared (NIR) fluorescence imaging >1,000 nm allows deep tissue imaging, but available organic dyes display poor brightness and temporal resolution. Here, the authors synthesize a NIR dye that, upon binding serum proteins, exhibits a 110-fold increase in intensity, giving an 11% quantum yield.

Nanoemitters and innate immunity: the role of surfactants and bio-coronas in myeloperoxidase-catalyzed oxidation of pristine single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) are experimentally utilized in in vivo imaging and photothermal cancer therapy owing to their unique physicochemical and electronic properties. For these applications, pristine carbon nanotubes are often modified by polymer surfactant coatings to improve their biocompatibility, adding more complexity to their recognition and biodegradation by immuno-competent cells. Here, we investigate the oxidative degradation of SWCNTs catalyzed by neutrophil myeloperoxidase (MPO) using bandgap near-infrared (NIR) photoluminescence and Raman spectroscopy. Our results show diameter-dependence at the initial stages of the oxidative degradation of sodium cholate-, DNA-, and albumin-coated SWCNTs, but not phosphatidylserine-coated SWCNTs. Moreover, sodium deoxycholate- and phospholipid-polyethylene glycol coated SWCNTs were not oxidized under the same reaction conditions, indicating that a surfactant can greatly impact the biodegradability of a nanomaterial. Our data also revealed that possible binding between MPO and surfactant coated-SWCNTs was unfavorable, suggesting that oxidation is likely caused by a hypochlorite generated through halogenation cycles of free MPO, and not MPO bound to the surface of SWCNTs. The identification of SWCNT diameters and coatings that retain NIR fluorescence during the interactions with the components of an innate immune system is important for their applications in in vivo imaging.