Implantable Nanotube Sensor Platform for Rapid Analyte Detection

Development of sterile platform for quantification of extracellular analytes via single walled carbon nanotubes

Progress has been made studying cell-cell signaling communication processes. However, due to limitations of current sensors on time and spatial resolution, the role of many extracellular analytes is still unknown. A single walled carbon nanotube (SWNT) platform was previously developed based on the avidin-biotin immobilization of SWNT to a glass substrate. The SWNT platform provides real time feedback about analyte concentration and has a high concentration of evenly distributed sensors, both of which are essential for the study of extracellular analytes. Unfortunately, this initial SWNT platform is synthesized through unsterile conditions and cannot be sterilized post-production due to the delicate nature of the sensors, making it unsuitable for in vitro work. Herein the multiple-step process for SWNT immobilization is modified and the platform's biocompatibility is assessed in terms of sterility, cytotoxicity, cell proliferation, and cell morphology through comparison with non-sensors controls. The results demonstrate the SWNT platform's sterility and lack of toxicity over 72 h. The proliferation rate and morphology profiles for cells growing on the SWNT platform are similar to those grown on tissue culture substrates. This novel nano-sensor platform preserves cell health and cell functionality over time, offering opportunities to study extracellular analytes gradients in cellular communication.

Single-walled carbon nanotubes as near-infrared fluorescent probes for bio-inspired supramolecular self-assembled hydrogels

Hydrogels derived from fluorenylmethoxycarbonyl (Fmoc)-conjugated amino acids and peptides demonstrate remarkable potential in biomedical applications, including drug delivery, tissue regeneration, and tissue engineering. These hydrogels can be injectable, offering a minimally invasive approach to hydrogel implantation. Given their potential for prolonged application, there is a need for non-destructive evaluation of their properties over extended periods. Thus, we introduce a hydrogel characterization platform employing single-walled carbon nanotubes (SWCNTs) as near-infrared (NIR) fluorescent probes. Our approach involves generating supramolecular self-assembling hydrogels from aromatic Fmoc-amino acids. Integrating SWCNTs into the hydrogels maintains their structural and mechanical properties, establishing SWCNTs as optical probes for hydrogels. We demonstrate that the SWCNT NIR-fluorescence changes during the gelation process correlate to rheological changes within the hydrogels. Additionally, single particle tracking of SWCNTs incorporated in the hydrogels provides insights into differences in hydrogel morphologies. Furthermore, the disassembly process of the hydrogels can be monitored through the SWCNT fluorescence modulation. The unique attribute of SWCNTs as non-photobleaching fluorescent sensors, emitting at the biologically transparent window, offers a non-destructive method for studying hydrogel dynamics over extended periods. This platform could be applied to a wide range of self-assembling hydrogels to advance our understanding and applications of supramolecular assembly technologies.

Development and Evaluation of an Expedited System for Creation of Single Walled Carbon Nanotube Platforms

Single-walled carbon nanotubes (SWNT) have a strong and stable near-infrared (nIR) fluorescence that can be used to selectively detect target analytes, even at the single molecule level, through changes in either their fluorescence intensity or emission peak wavelength. SWNTs have been employed as NIR optical sensors for detecting a variety of analytes. However, high costs, long fabrication times, and poor distributions limit the current methods for immobilizing SWNT sensors on solid substrates. Recently, our group reported a protocol for SWNT immobilization with high fluorescence yield, longevity, fluorescence distribution, and sensor response, unfortunately this process takes 5 days to complete. Herein we report an improved method to immobilize SWNT sensors that only takes 2 days and results in higher fluorescence intensity while maintaining a high level of SWNT distribution. We performed surface morphology and chemical composition tests on the original and new synthesis methods and compared the sensor response rates. The development of this new method of attaching SWNT sensors to a platform allows for creation of a sensing system in just 2 days without sacrificing the advantageous characteristics of the original, 5-day platforms.

Stimuli-bioresponsive hydrogels as new generation materials for implantable, wearable, and disposable biosensors for medical diagnostics: Principles, opportunities, and challenges

Hydrogels are excellent water-swollen polymeric materials for use in wearable, implantable, and disposable biosensors. Hydrogels have unique properties such as low cost, ease of preparation, transparency, rapid response to external conditions, biocompatibility and self-adhesion to the skin, flexibility, and strain sensitivity, making them ideal for use in biosensor platforms. This review provides a detailed overview of advanced applications of stimuli-responsive hydrogels in biosensor platforms, from hydrogel synthesis and functionalization for bioreceptor immobilization to several important diagnostic applications. Emphasis is placed on recent advances in the fabrication of ultrasensitive fluorescent and electrically conductive hydrogels and their applications in wearable, implantable, and disposable biosensors for quantitative measurements. Design, modification, and assembly techniques of fluorescent, ionically conductive, and electrically conductive hydrogels to improve performance will be addressed. The advantages and performance improvements of immobilizing bioreceptors (e.g., antibodies, enzymes, and aptamers), and incorporating fluorescent and electrically conductive nanomaterials are described, as are their limitations. Potential applications of hydrogels in implantable, wearable, disposable portable biosensors for quantitative detection of the various bioanalytes (ions, molecules, drugs, proteins, and biomarkers) are discussed. Finally, the global market for hydrogel-based biosensors and future challenges and prospects are discussed in detail.

Bioengineering a glucose oxidase nanosensor for near-infrared continuous glucose monitoring

Single-walled carbon nanotubes (SWCNTs) emit photostable near-infrared (NIR) fluorescence that is conducive for optical glucose monitoring. Such SWCNT-based optical sensors often require the immobilization of proteins that can confer glucose selectivity and reactivity. In this work, we immobilize a glucose-reactive enzyme, glucose oxidase (GOx), onto SWCNTs using a N-(1-pyrenyl)maleimide (PM) crosslinker via thiol bioconjugation of engineered cysteine residues. We compare the conjugation of several glucose oxidase variants containing rationally-engineered cysteines and identify a D70C variant that shows effective bioconjugation. The bioconjugation was characterized through both absorption and fluorescence spectroscopy. Furthermore, we demonstrate an application for continuous glucose monitoring in the NIR-II optical region using the bioconjugated reaction solution, which shows a reversible response to physiological concentrations of glucose. Finally, we develop a miniaturized NIR-II reader to be used for cell cultures that require continuous glucose monitoring.

Single-Walled Carbon Nanotube-Based Biosensors for Detection of Bronchial Inflammation

Inflammation is a protective mechanism against invading pathogens and tissue damage. However, the inflammatory process is implicated in a wide range of diseases affecting all organs and body systems. Nitric oxide — a multifunctional signaling molecule that plays a critical role in systemic blood pressure homeostasis, prevention of platelet aggregation, antimicrobial resistance, immunoregulation, tumor suppression and as a neurotransmitter — is used as a surrogate marker for inflammation. However, the most commonly used Griess assay is an indirect and expensive method for the determination of nitric oxide concentration. Hence, single-walled carbon nanotube-based biosensors have been explored as real-time, sensitive, selective and safe methods to determine nitric oxide released during the inflammatory process. In this review, we explore current developments in single-walled carbon nanotube-based biosensors for the detection of nitric oxide in exhaled breath as a direct and noninvasive test for detection of bronchial inflammation.

Novel methods to extract and quantify sensors based on single wall carbon nanotube fluorescence from animal tissue and hydrogel-based platforms

Sensors that can quickly and accurately diagnose and monitor human health are currently at the forefront of medical research. Single walled carbon nanotube (SWNT) based optical biosensors are a growing area of research due to the high spatiotemporal resolution of their near infrared fluorescence leading to high tissue transparency and unparalleled sensitivity to analytes of interest. Unfortunately, due to the functionalization requirements of SWNT-based sensors, there are concerns surrounding accumulation and persistence when applied in vivo. In this study, we developed protocols to extract and quantify SWNT from complex solutions and show an 89% sensor retention by hydrogel platforms when implanted in vivo. Animal tissues of interest were also extracted and probed for SWNT content showing no accumulation (0.03 mg l^-1 SWNT detection limit). The methods developed in this paper demonstrated one avenue for applying SWNT sensors in vivo without concern for accumulation.

Single-Walled Carbon Nanotube Sensor Platform for the Study of Extracellular Analytes

Single-walled carbon nanotubes (SWNT) are attractive targets for the formation of high-density sensor arrays. Their small size and high reactivity could allow for the spatial and temporal study of extracellular products to a degree which greatly surpasses contemporary sensors. However, current methods of SWNT immobilization produce a low fluorescence yield that requires a combination of high magnification, exposure time, and laser intensity to combat, thus limiting the sensor's applications. In this work, a platform for the immobilization of SWNT sensors with increased fluorescence yield, longevity, fluorescence distribution, and fast reaction times is developed.

Fluorescent Single-Walled Carbon Nanotubes for Protein Detection

Nanosensors have a central role in recent approaches to molecular recognition in applications like imaging, drug delivery systems, and phototherapy. Fluorescent nanoparticles are particularly attractive for such tasks owing to their emission signal that can serve as optical reporter for location or environmental properties. Single-walled carbon nanotubes (SWCNTs) fluoresce in the near-infrared part of the spectrum, where biological samples are relatively transparent, and they do not photobleach or blink. These unique optical properties and their biocompatibility make SWCNTs attractive for a variety of biomedical applications. Here, we review recent advancements in protein recognition using SWCNTs functionalized with either natural recognition moieties or synthetic heteropolymers. We emphasize the benefits of the versatile applicability of the SWCNT sensors in different systems ranging from single-molecule level to in-vivo sensing in whole animal models. Finally, we discuss challenges, opportunities, and future perspectives.