Significance: Personalized medicine requires the tracking of an individual’s metabolite levels over time to detect anomalies and evaluate the body’s response to medications. Implanted sensors offer effective means to continuously monitor specific metabolite levels, provided they are accurate, stable over long time periods, and do no harm.
Aim: Four types of hydrogel embedded with pH-sensitive sensors were evaluated for their accuracy, sensitivity, reversibility, longevity, dynamic response, and consistency in static versus dynamic conditions and long-term storage.
Approach: Raman spectroscopy was first used to calibrate the intensity of pH-sensitive peaks of the Raman-active hydrogel sensors in a static pH environment. The dynamic response was then assessed for hydrogels exposed to changing pH conditions within a flow cell. Finally, the static pH response after 5 months of storage was determined.
Results: All four types of hydrogels allowed the surface-enhanced Raman spectroscopy (SERS) sensors to respond to the pH level of the local environment without introducing interfering signals, resulting in consistent calibration curves. When the pH level changed, the probes in the gels were slow to reach steady-state, requiring several hours, and response times were found to vary among hydrogels. Only one type, poly(2-hydroxyethyl methacrylate) (pHEMA), lasted five months without significant degradation of dynamic range.
Conclusions: While all hydrogels appear to be viable candidates as biocompatible hosts for the SERS sensing chemistry, pHEMA was found to be most functionally stable over the long interval tested. Poly(ethylene glycol) hydrogels exhibit the most rapid response to changing pH. Since these two gel types are covalently cross-linked and do not generally degrade, they both offer advantages over sodium alginate for use as implants.
Now that a fully-implantable, continuous glucose monitor has received FDA approval, optical techniques other than fluorescence will seek to overcome the limited lifetimes resulting from photobleaching. Using plasmonic nanoparticles, we present the potential of reversible SERS-active sensing assays to function as long-term implantable sensors. The assays offer high selectivity and specificity of analyte detection and concentration without loss of emission intensity over time due to photodestruction. These assays are encapsulated in microdomains bounded by polyelectrolyte multilayers (PEMs), permeable to the target but impermeable to proteins. The microdomains are stabilized in hydrogels for biocompatibility and longevity. This study characterizes the performance of pH-sensitive Raman probes in three different hydrogels in a simulated in vivo environment with changing pH over time.
A Matlab front end to the LACE Adaptive Optics Performance Analysis program has been developed. The software can be run on any system that has the Matlab software installed. The graphical user interface for LACE is used to set the input parameters, to initiate execution, to monitor error messages during execution and to graphically illustrate the outputs of an individual runs as well as results over time.
The new generation of 21st century 8m ground-based telescopes requires a new model of proposal submission. The proposal submission tool must be globally accessible and provide an efficient mechanisms to create a proposal and submit it for review. Global accessibility is dependent on network availability and connection time should be minimized to reduce this dependency. The efficiency of the tool is optimized by implementing checks which ensure that the proposal is complete before it reaches the reviewers. This saves the reviewers form having to contact the astronomer for additional information and the astronomer is assured that her/his proposal will not be rejected for its incompleteness. The Gemini Phase 1 Science Proposal Entry Tool is a platform-independent software program which is downloaded from the web to reside on the astronomer's local machine. During the creation of a science proposal, no network connection is required.Input is entered through a Graphical User Interface (GUI) which consists of a series of pages. The astronomer can, for the most part, page around the GUI entering the information in any order. However, in some case, data that determines what is displayed on other pages must be entered before advancing to the next page. Local saves and prints of the proposal can be made at any time. Also, the tool can reload an existing proposal so that the astronomer can work on a proposal over several sittings. Completed pages are indicated on a floating screen separate from the main GUI. When the astronomer is ready to submit the proposal, the file is verified for completeness. If compete, it is submitted to the National Time Allocation Committee via ftp.
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