Search

Minimally invasive devices to detect molecules in dermal interstitial fluid (ISF) are desirable for point-of-care diagnostic and monitoring applications. In this study, we developed a microneedle (MN) patch that collects ISF for on-patch biomarker analysis by surface-enhanced Raman scattering (SERS). The micrometer-scale MNs create micropores in the skin surface, through which microliter quantities of ISF are collected onto plasmonic paper on the patch backing. The plasmonic paper was prepared by immobilizing poly(styrenesulfonate) (PSS) coated gold nanorods (AuNRs) on a thin strip of filter paper using plasmonic calligraphy. Negatively charged PSS was used to bind positively charged rhodamine 6G (R6G), which served as a model compound, and thereby localize R6G on AuNR surface. R6G bound on the AuNR surface was detected and quantified by acquiring SERS spectra from the plasmonic paper MN patch. This approach was used to measure pharmacokinetic profiles of R6G in ISF and serum from rats in vivo. This proof-of-concept study indicates that a plasmonic paper MN patch has the potential to enable on-patch measurement of molecules in ISF for research and future medical applications.

Objectives: To determine whether factors associated with postural tremor operate by altering muscle interstitial K+. Methods: An experimental approach was used to investigate the effects of procedures designed to increase or decrease interstitial K+. Postural physiological tremor was measured by conventional means. Brief periods of ischaemic muscle activity were used to increase muscle interstitial K+. Infusion of the s2 agonist terbutaline was used to decrease plasma (and interstitial) K+. Blood samples were taken for the determination of plasma K+. Results: Ischaemia rapidly reduced tremor size, but only when the muscle was active. The s2 agonist produced a slow and progressive rise in tremor size that was almost exactly mirrored by a slow and progressive decrease in plasma K+. Conclusions: Ischaemic reduction of postural tremor has been attributed to effects on muscle spindles or an unexplained effect on muscle. This study showed that ischaemia did not reduce tremor size unless there was accompanying muscular activity. An accumulation of K+ in the interstitium of the ischaemic active muscle may blunt the response of the muscle and reduce its fusion frequency, so that the force output becomes less pulsatile and tremor size decreases. When a s2 agonist is infused, the rise in tremor mirrors the resultant decrease in plasma K+. Decreased plasma K+ reduces interstitial K+ concentration and may produce greater muscular force fluctuation (more tremor). Many other factors that affect postural tremor size may exert their effect by altering plasma K+ concentration, thereby changing the concentration of K+ in the interstitial fluid.