Design of composite microneedle sensor systems for the measurement of transdermal pH

Abstract

Carbon loaded polystyrene microneedle patches have been prepared using silicone micromoulding techniques and the ability of the needles to serve as viable transdermal sensors has been evaluated. The population of quinone groups at the interface of the embedded carbon nanoparticles was increased through anodisation and their pH dependent redox transitions exploited as the basis of a reagentless pH sensor. The peak position of the quinone oxidation process was found to shift in accordance with Nernstian behaviour and the influence of penetration depth on response has been investigated. The analytical applicability of the microneedle electrode patch was critically evaluated through using tomato skin as model transdermal skin mimic. Despite the increased complexity of the matrix, the microneedle sensor response was found to compare favourably with conventional/commercial pH probes.

Probing the pH Microenvironment of Mesenchymal Stromal Cell Cultures on Additive‐Manufactured Scaffolds

“…However, their application is generally limited to analysis in bulk structures such as brain fluid, intestine, bladder, and skin. [ 31–34 ] These systems require big volumes of culture medium and often compromise the sterility of the experiment. [ 35 ]…”

“…However, their application is generally limited to analysis in bulk structures such as brain fluid, intestine, bladder, and skin. [31][32][33][34] These systems require big volumes of culture medium and often compromise the sterility of the experiment. [35] To circumvent these problems, fluorescent sensors have been developed to study the metabolic state at a cell size scale and to provide a real-time detection of acidification basing on the changes of fluorescence intensity induced by pH variations.…”

Composite Microneedle Arrays Modified With Palladium Nanoclusters for Electrocatalytic Detection of Peroxide

“…Electrochemical anodisation (+2 V, 0.1 M NaOH) was performed on the carbon based MN patches in order to promote the formation of interfacial carboxyl groups necessary for the capture of the palladium ions [8,9]. Oxidation of carbon fibers and the production of a large variety of chemical moieties (Fig 1) is well established and it was expected that a similar process would result with the carbon composite formulation used in the production of the needles.…”

“…The development of microneedle (MN) arrays as a minimally invasive method of drug delivery [1][2][3] is well established but it is only in recent years however, that the underpinning technologies used to produce such arrays have been adapted for the development of transdermal sensors. The metalization of silicon or polymeric needles with gold or platinum has already been investigated for use in a variety of biosensing applications [4][5][6][7] but micro-molding techniques have been shown to offer a more rapid prototyping option within conventional laboratory settings [8][9][10]. The incorporation of nanomaterials into a suitable polymer composite matrix (typically polystyrene) can allow tailored applications and, in the case of carbon nanoparticles, conductive sensors with a rich surface chemistry ripe for further modification.…”

“…This approach relies on nano-structuring the carbon surface through the electrochemical exfoliation of the interfacial carbon nanoparticles that comprise the conductive elements within the array [8,9]. This should have the effect of increasing both the proportion of edge plane sites and the population of oxygen functionalitiesprincipally carboxylate groups.…”