Toxicity assessment of wearable wound sensor constituents on keratinocytes

Second Skin as Self-Protection Against γ-Hydroxybutyrate

γ-Hydroxybutyrate (GHB), a date-rape drug, causes certain symptoms, such as amnesia, confusion, ataxia, and unconsciousness, when dissolved in beverages and consumed by a victim. Commonly, assailants use GHB in secret for the crime of drug-facilitated sexual assault because it is tasteless, odorless, and colorless when dissolved in beverages. Generally, GHB detection methods are difficult to use promptly and secretly in situ and in real life because of the necessary detection equipment and low selectivity. To overcome this problem, we have developed a fast, simple, and easy-to-use second skin platform as a confidential self-protection platform that can detect GHB in situ or in real life without equipment. The second skin platform for naked-eye detection of GHB is fabricated with poly(vinyl alcohol) (PVA), polyurethane (PU), and polyacrylonitrile (PAN) included in the chemical receptor 2-(3-bromo-4-hydroxystyryl)-3-ethylbenzothiazol-3-ium iodide (BHEI). PAN conjugated with BHEI nanofibers (PB NFs) has various characteristics, such as ease of use, high sensitivity, and fast color change. PB NFs rapidly detected GHB at 0.01 mg/mL. Furthermore, the second-skin platform attached to the fingertip and wrist detected both 1 and 0.1 mg/mL GHB in solution within 50 s. The color changes caused by the interaction of GHB and the second skin platform cannot be stopped due to strong chemical reactions. In addition, a second skin platform can be secretly utilized in real life because it can recognize fingerprints and object temperatures. Therefore, the second skin platform can be used to aid daily life and prevent drug-facilitated sexual assault crime when attached to the skin because it can be exposed anytime and anywhere.

The Evolving Role of Proteins in Wearable Sweat Biosensors

Sweat is an increasingly popular biological medium for fitness monitoring and clinical diagnostics. It contains an abundance of biological information and is available continuously and noninvasively. Sweat-sensing devices often employ proteins in various capacities to create skin-friendly matrices that accurately extract valuable and time-sensitive information from sweat. Proteins were first used in sensors as biorecognition elements in the form of enzymes and antibodies, which are now being tuned to operate at ranges relevant for sweat. In addition, a range of structural proteins, sometimes assembled in conjunction with polymers, can provide flexible and compatible matrices for skin sensors. Other proteins also naturally possess a range of functionalities─as adhesives, charge conductors, fluorescence emitters, and power generators─that can make them useful components in wearable devices. Here, we examine the four main components of wearable sweat sensors─the biorecognition element, the transducer, the scaffold, and the adhesive─and the roles that proteins have played so far, or promise to play in the future, in each component. On a case-by-case basis, we analyze the performance characteristics of existing protein-based devices, their applicable ranges of detection, their transduction mechanism and their mechanical properties. Thereby, we review and compare proteins that can readily be used in sweat sensors and others that will require further efforts to overcome design, stability or scalability challenges. Incorporating proteins in one or multiple components of sweat sensors could lead to the development and deployment of tunable, greener, and safer biosourced devices.

Carbon Dot-Doped Hydrogel Sensor Array for Multiplexed Colorimetric Detection of Wound Healing

Effective wound care and treatment require a quick and comprehensive assessment of healing status. Here, we develop a carbon dot-doped hydrogel sensor array in polydimethylsiloxane (PDMS) for simultaneous colorimetric detections of five wound biomarkers and/or wound condition indicators (pH, glucose, urea, uric acid, and total protein), leading to the holistic assessment of inflammation and infection. A biogenic carbon dot synthesized using an amino acid and a polymer precursor is doped in an agarose hydrogel matrix for constructing enzymatic sensors (glucose, urea, and uric acid) and dye-based sensors (pH and total protein). The encapsulated enzymes in such a matrix exhibit improved enzyme kinetics and stability compared to those in pure hydrogels. Such a matrix also provides stable colorimetric responses for all five sensors. The sensor array exhibits high accuracy (recovery rates of 91.5-113.1%) and clinically relevant detection ranges for all five wound markers. The sensor array is established for simulated wound fluids and validated with rat wound fluids from perturbed wound models. Distinct color patterns are obtained that can clearly distinguish healing vs nonhealing wounds visually and quantitatively. This hydrogel sensor array shows great potential for on-site wound sensing due to its long-term stability, lightweight, and flexibility.

Bio-acceptability of wearable sensors: a mechanistic study towards evaluating ionic leaching induced cellular inflammation

The recent need for remote health wellness monitoring has led to the extensive use of wearable sensors. Owing to their increased use, these sensors are required to exhibit both functionality and safety to the user. A major component in the fabrication of these sensors and their associated circuitry is the use of metallic/organic conductive inks. However, very less is known about the interfacial and molecular interactions of these inks with biological matter as they can result in an inflammatory reaction to the user. Significant efforts are thus needed to explore and improve the bio-acceptability of such conductive ink-based wearable sensors. The present study investigates the biocompatibility of encapsulated and non-encapsulated wearable electrochemical sensors used for sensing uric acid as a biomarker for wound healing fabricated using screen-printing technique. Ionic release of metallic ions was investigated first to understand the susceptibility of the conductive inks towards ionic leaching when in contact with a fluid. Time-lapse investigation using ICPS (inductive couple plasma spectroscopy) shows a high concentration (607.31 ppb) of leached silver (Ag⁺) ions from the non-encapsulated sensors. The cell viability data suggests a 2.5-fold improvement in the sensor biocompatibility for an encapsulated sensor. While the carbon ink shows negligible effect on cell viability, the silver ink elicits significant decrease (< 50%) in cell viability at concentrations higher than 2 mg ml^-1. The toxicity pathway of these sensors was further determined to be through the generation of reactive oxygen species resulting in over 20% apoptotic cell death. Our results show that the lower biocompatibility of the non-encapsulated sensor attributes to the higher leaching of Ag⁺ ions from the printed inks which elicits several different inflammatory pathways. This work highlights the importance biocompatibility evaluation of the material used in sensor fabrication to develop safe and sustainable sensors for long-term applications.

Characterization of ionic liquid cytotoxicity mechanisms in human keratinocytes compared with conventional biocides

The ability to chemically modify ionic liquids (ILs) has led to an expansion in interest in their use in a diversity of applications, not least as antimicrobials and biocides. Relatively little is known about cytotoxicity mechanisms of ILs in comparison to other biocides currently in widespread use, as well as their practical significance for the ecological environment and human health. Using NCTC 2544 and HaCat human keratinocyte cells, this study aimed to characterize cytotoxicity rates and mechanisms of a range of ILs. Using both lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) based cytotoxicity assays, it was confirmed that at biocide-relevant concentrations, ILs with longer alkyl chains exhibited greater biocidal activity than those with shorter alkyl chains, with comparable activity to the commonly used biocides chlorhexidine, benzalkonium chloride and cetylpyridinium chloride, at relevant in-use biocide concentrations. Mode of cell death, measured using fluorescence-activated cell sorting (FACS) and caspase 3/7 activity, determined necrosis to be the primary cytotoxic mechanism at higher concentrations of the biocides stated above, and with ILs [C₁₄MIM]Cl and [C₁₄quin]Br, with apoptosis observed at borderline necrotic concentrations. Perhaps most interestingly, modification of anion had a significant effect on cytotoxicity. The use of N[SO₂CF₃] as an anion to [C₁₆MIM] attenuated cytotoxicity 10-fold in comparison to other anions, suggesting cytotoxicity may also be a tuneable property when using ILs as biocides.

Small-volume detection: platform developments for clinically-relevant applications

Biochemical analysis of human body fluids is a frequent and fruitful strategy for disease diagnosis. Point-of-care (POC) diagnostics offers the tantalizing possibility of providing rapid diagnostic results in non-laboratory settings. Successful diagnostic testing using body fluids has been reported on in the literature; however, small-volume detection devices, which offer remarkable advantages such as portability, inexpensiveness, capacity for mass production, and tiny sample volume requirements have not been thoroughly discussed. Here, we review progress in this research field, with a focus on developments since 2015. In this review article, we provide a summary of articles that have detailed the development of small-volume detection strategies using clinical samples over the course of the last 5 years. Topics covered include small-volume detection strategies in ophthalmology, dermatology or plastic surgery, otolaryngology, and cerebrospinal fluid analysis. In ophthalmology, advances in technology could be applied to examine tear or anterior chamber (AC) fluid for glucose, lactoferrin, interferon, or VEGF. These approaches could impact detection and care for diseases including diabetic mellitus, dry-eye disease, and age-related maculopathy. Early detection and easy monitoring are critical approaches for improving overall care and outcome. In dermatology or plastic surgery, small-volume detection strategies have been applied for passive or interactive wound dressing, wound healing monitoring, and blister fluid analysis for autoimmune disease diagnosis. In otolaryngology, the analysis of nasal secretions and mucosa could be used to differentiate between allergic responses and infectious diseases. Cerebrospinal fluid analysis could be applied in neurodegenerative diseases, central neural system infection and tumor diagnosis. Other small-volume fluids that have been analyzed for diagnostic and monitoring purposes include semen and cervico-vaginal fluids. We include more details regarding each of these fluids, associated collection and detection devices, and approaches in our review.

Miconazole and terbinafine induced reactive oxygen species accumulation and topical toxicity in human keratinocytes

There are an estimated 1 billion cases of superficial fungal infection globally. Fungal pathogens form biofilms within wounds and delay the wound healing process. Miconazole and terbinafine are commonly used to treat fungal infections. They induce the accumulation of reactive oxygen species (ROS) in fungi, resulting in the death of fungal cells. ROS are highly reactive molecules, such as oxygen (O₂), superoxide anion (O₂•-), hydrogen peroxide (H₂O₂) and hydroxyl radicals (•OH). Although ROS generation is useful for killing pathogenic fungi, it is cytotoxic to human keratinocytes. To the best of our knowledge, the effect of miconazole and terbinafine on HaCaT cells has not been studied with respect to intracellular ROS stimulation. We hypothesized that miconazole and terbinafine have anti-wound healing effects on skin cells when used in antifungal treatment because they generate ROS in fungal cells. We used sulforhodamine B protein staining to investigate cytotoxicity and 2',7'-dichlorofluorescein diacetate to determine ROS accumulation at the 50% inhibitory concentrations of miconazole and terbinafine in HaCaT cells. Our preliminary results showed that topical treatment with miconazole and terbinafine induced cytotoxic responses, with miconazole showing higher cytotoxicity than terbinafine. Both the treatments stimulated ROS in keratinocytes, which may induce oxidative stress and cell death. This suggests a negative correlation between intracellular ROS accumulation in keratinocytes treated with miconazole or terbinafine and the healing of fungi-infected skin wounds.