Microscale Enzymatic Optical Biosensors Using Mass Transport Limiting Nanofilms. 1. Fabrication and Characterization Using Glucose as a Model Analyte

Abstract

Abstract"Smart tattoo" sensors -fluorescent microspheres which can be implanted intradermally and interrogated noninvasively using light -are being developed as potential tools for in vivo biochemical monitoring. In this work, a platform for enzymatic tattoo-type sensors is described, and prototype devices evaluated using glucose as a model analyte. Sensor particles were prepared by immobilizing Pt(II) octaethylporphine (PtOEP), a phosphorescent dye readily quenched by molecular oxygen, into hybrid silicate microspheres, followed by loading and subsequent covalent immobilization of glucose oxidase (GOx). Rhodamine B (RITC)-doped multilayer nanofilms were subsequently assembled on the surfaces of the particles to provide a reference signal and provide critical control of glucose transport into the particle. The enzymatic oxidation of glucose within the sensor results in the glucose concentration-dependent depletion of local oxygen levels, enabling indirect monitoring of glucose by measuring relative changes in PtOEP emission. A custom testing apparatus was used to monitor the dynamic sensor response to varying bulk oxygen and glucose levels, respectively. For the prototypes tested, dynamic test results indicate that the sensors respond rapidly (t 95 = 84 sec) and reversibly to changes in bulk glucose levels, while demonstrating high baseline stability. The sensitivity (change in intensity ratio) of these devices was determined to be 4.16 ± 0.57 %/mg dL −1 . The analytical range for the prototypes was determined to be 2 to 120 mg/dl, though this can be extended to cover the physiologically relevant range by tailoring the nanofilm coatings. These findings confirm the potential for enzymatic microscale optical, and pave the way for extension of this initial demonstration with glucose to target other biochemical species relevant to metabolic monitoring.

Preclinical Evaluation of Poly(HEMA-co-acrylamide) Hydrogels Encapsulating Glucose Oxidase and Palladium Benzoporphyrin as Fully Implantable Glucose Sensors

“…[13][14][15] Demonstrations of potential hydrogel sensor formats over the years have included poly(ethylene glycol)-based microspheres and fibers [13][14][15] and includes a variety of hollow polymeric capsules and various nanocomposite particulate systems using other encapsulating materials. [16][17][18][19][20] Utilizing these unique properties of hydrogels in a fully implantable CGM may circumvent repetitive tissue trauma and infection associated with the percutaneous nature of traditional CGM devices in vivo. 9,21 Used in medical devices for decades, one of the most widely studied and well-characterized hydrogels for biomedical applications is poly (2-hydroxyethyl methacrylate) (pHEMA).…”

“…Sensor response depends on the availability of the substrates glucose and oxygen to the enzyme (governed by mass transport) as well as the affinity of the enzyme for both substrates. 16,19,20,26,27 We have previously shown that pHEMA-based hydrogels can be functionalized with enzymes and long-lifetime phosphors to be used as luminescence-based glucose sensors. In the same study, we illustrated the ability to tune sensor behavior through hydrogel composition by influencing glucose and oxygen diffusion.…”

Materiomics for Oral Disease Diagnostics and Personal Health Monitoring: Designer Biomaterials for the Next Generation Biomarkers

“…Enzymatic biosensor, introduced by Clark and Lyons when they built the first glucose biosensor in 1962 (Clark and Lyons, 1962), is a very popular field in bioanalytical applications witnessing tremendous work done over the past 50 years (Odaci et al, 2009;Stein et al, 2007;Wilson and Turner, 1992). Enzymes are the most used biocatalytic elements enabling the detection of analytes in various ways, such as measuring the consumed or produced species after the enzymatic reactions (Gough et al, 1985;Guilbault and Lubrano, 1973;Reach and Wilson, 1992) or tracking the electrons passed through the electrodes during reactions (Holland et al, 2011;Shan et al, 2009;Si et al, 2011;Wang, 2008).…”

Nanofilm coatings for transport control and biocompatibility

“…[14,15] We applied the Layer-by-Layer (LbL) self-assembly technique for nanofilm construction, due to the flexibility of the approach to create composite films with nanometer resolution. [16][17][18][19][20] Recently, a series of reports described the transport of various molecular species through polyelectrolyte multilayers.…”

“…[21] Exploiting this extraordinarily low glucose diffusivity and precision for assembly, we showed that LbL films can be applied as tunable diffusion-limiting coatings for optical biosensors. [14,15] To further make sensors appropriate for in vivo deployment, it is essential to create an interface with the biological system that minimizes the response to the foreign material, such as inflammation and immune system attack. Protein adsorption is the initial event that mediates host response to foreign materials.…”