Abstract
.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.
Highlights
Personalized medicine has been predicted to be disruptive, eventually upending the medical industry by shifting expenditures from reactionary to preventative care.[1]
Each step of the fabrication process consists of seven sub-steps related to acquisition and processing, with results included in the Supplementary Material
This work evaluated the performance of SERS-based pH sensors using microencapsulated AuNPs embedded in different hydrogels
Summary
Personalized medicine has been predicted to be disruptive, eventually upending the medical industry by shifting expenditures from reactionary to preventative care.[1]. Expanding the set of tools to enable tracking a range of metabolites and storing these values in personal electronic medical and other accessible records is the first step.[6] For convenience, comfort, and value, such devices must enable frequent, facile sampling and possess a long operating lifetime, which is especially challenging for implanted devices.[7] Optical methods offer promise for minimally invasive monitoring but must be built on stable, reversible transduction chemistry, and biocompatible packaging. There are both elastic (Rayleigh) and inelastic (Raman) techniques. Fluorescence-based sensors detect photons reemitted at lower energies after absorption by special chromophores, and typically lose sensitivity over time due to photobleaching.[8] In contrast, Raman spectroscopy (RS) offers potential to extend the operating lifetime of a sensor, by working at a lower energy which does not degrade the materials by photobleaching. The very low efficiency of Raman inelastic scattering (compared to elastic scattering) limits its usefulness
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