Flexible Optical Fiber Sensor for Non-Invasive Continuous Monitoring of Human Physiological Signals

With increasing health awareness, monitoring human physiological signals for health status and disease prevention has become crucial. Non-invasive flexible wearable devices address issues like invasiveness, inconvenience, size, and continuous monitoring challenges in traditional devices. Among flexible sensors, optical fiber sensors (OFSs) stand out due to their excellent biocompatibility, anti-electromagnetic interference capabilities, and ability to monitor multiple signals simultaneously. This paper reviews the application of flexible optical fiber sensing technology (OFST) in monitoring human lung function, cardiovascular function, body parameters, motor function, and various physiological signals. It emphasizes the importance of continuous monitoring in personal health management, clinical settings, sports training, and emergency response. The review discusses challenges in OFST for continuous health signal monitoring and envisions its significant potential for future development. This technology underscores the importance of constant health signal monitoring and highlights the advantages and prospects of optical fiber sensing. Innovations in OFS for non-invasive continuous monitoring of physiological signals hold profound implications for materials science, sensing technology, and biomedicine.

A novel multifunctional fluorescent capillary-based sensor for simultaneous monitoring of pH, O2 and CO2

A fluorescent capillary sensor for detecting the bioanalytically and biologically relevant analytes pH, O2, and CO2 has been designed. The sensor is based on single capillary tube with 2 mm inner diameter, which is simultaneous doped with emissive O2-sensitive indicator Ru(dpp)3(PF6)2 (RuDP), pH-sensitive and CO2-sensitive indicator 8-hydroxypyrene-1, 3,6-trisulfonic acid trisodium salt (HPTS). The multifunctional sensor can be excited at the same wavelength and realize multi-parameter optical monitoring at the different sensing position. Studies in phosphate-buffered solutions display the excellent feasibility of the capillary sensor for fluorescence detection of pH, O2, and CO2. Overall, the multifunctional capillary sensor exhibits great potential in real-time blood gas analysis, and clinical application of multi-parameter biological detection.

Specially Designed Polyaniline/Polypyrrole Ink for a Fully Printed Highly Sensitive pH Microsensor

pH sensing for healthcare applications requires sensors with mechanically stable materials of high sensitivity and high reproducibility combined with low-cost fabrication technologies. This work proposes a fully printed pH sensor based on a specially formulated conducting polymer deposited on a microelectrode in a flexible substrate. A formulation, which combined polyaniline (PANI) and polypyrrole (PPy) with integrated polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), was specially prepared to be printed by inkjet printing (IJP). The sensor has good sensitivity in the physiological region (pH 7-7.5) key for the healthcare biosensor. This mixture printed over a commercial gold ink, which has a singular chemical functionalization with phthalocyanine (Pc), increased the sensor sensitivity, showing an excellent reproducibility with a linear super-Nernstian response (81.2 ± 0.5 mV/pH unit) in a wide pH range (pH 3-10). This new ink together with the IJP low-cost technique opens new opportunities for pH sensing in the healthcare field with a single device, which is disposable, highly sensitive, and stable in the whole pH range.

Non-invasive monitoring of pH and oxygen using miniaturized electrochemical sensors in an animal model of acute hypoxia

Background

One of the most prevalent causes of fetal hypoxia leading to stillbirth is placental insufficiency. Hemodynamic changes evaluated with Doppler ultrasound have been used as a surrogate marker of fetal hypoxia. However, Doppler evaluation cannot be performed continuously. As a first step, the present work aimed to evaluate the performance of miniaturized electrochemical sensors in the continuous monitoring of oxygen and pH changes in a model of acute hypoxia-acidosis.

Methods

pH and oxygen electrochemical sensors were evaluated in a ventilatory hypoxia rabbit model. The ventilator hypoxia protocol included 3 differential phases: basal (100% FiO₂), the hypoxia-acidosis period (10% FiO₂) and recovery (100% FiO₂). Sensors were tested in blood tissue (ex vivo sensing) and in muscular tissue (in vivo sensing). pH electrochemical and oxygen sensors were evaluated on the day of insertion (short-term evaluation) and pH electrochemical sensors were also tested after 5 days of insertion (long-term evaluation). pH and oxygen sensing were registered throughout the ventilatory hypoxia protocol (basal, hypoxia-acidosis, and recovery) and were compared with blood gas metabolites results from carotid artery catheterization (obtained with the EPOC blood analyzer). Finally, histological assessment was performed on the sensor insertion site. One-way ANOVA was used for the analysis of the evolution of acid-based metabolites and electrochemical sensor signaling results; a t-test was used for pre- and post-calibration analyses; and chi-square analyses for categorical variables.

Results

At the short-term evaluation, both the pH and oxygen electrochemical sensors distinguished the basal and hypoxia-acidosis periods in both the in vivo and ex vivo sensing. However, only the ex vivo sensing detected the recovery period. In the long-term evaluation, the pH electrochemical sensor signal seemed to lose sensibility. Finally, histological assessment revealed no signs of alteration on the day of evaluation (short-term), whereas in the long-term evaluation a sub-acute inflammatory reaction adjacent to the implantation site was detected.

Conclusions

Miniaturized electrochemical sensors represent a new generation of tools for the continuous monitoring of hypoxia-acidosis, which is especially indicated in high-risk pregnancies. Further studies including more tissue-compatible material would be required in order to improve long-term electrochemical sensing.

Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

This is the first comprehensive review on methods and materials for use in optical sensing of pH values and on applications of such sensors. The Review starts with an introduction that contains subsections on the definition of the pH value, a brief look back on optical methods for sensing of pH, on the effects of ionic strength on pH values and pKa values, on the selectivity, sensitivity, precision, dynamic ranges, and temperature dependence of such sensors. Commonly used optical sensing schemes are covered in a next main chapter, with subsections on methods based on absorptiometry, reflectometry, luminescence, refractive index, surface plasmon resonance, photonic crystals, turbidity, mechanical displacement, interferometry, and solvatochromism. This is followed by sections on absorptiometric and luminescent molecular probes for use pH in sensors. Further large sections cover polymeric hosts and supports, and methods for immobilization of indicator dyes. Further and more specific sections summarize the state of the art in materials with dual functionality (indicator and host), nanomaterials, sensors based on upconversion and 2-photon absorption, multiparameter sensors, imaging, and sensors for extreme pH values. A chapter on the many sensing formats has subsections on planar, fiber optic, evanescent wave, refractive index, surface plasmon resonance and holography based sensor designs, and on distributed sensing. Another section summarizes selected applications in areas, such as medicine, biology, oceanography, bioprocess monitoring, corrosion studies, on the use of pH sensors as transducers in biosensors and chemical sensors, and their integration into flow-injection analyzers, microfluidic devices, and lab-on-a-chip systems. An extra section is devoted to current challenges, with subsections on challenges of general nature and those of specific nature. A concluding section gives an outlook on potential future trends and perspectives.

Factors Influencing Motivation and Engagement in Mobile Health Among Patients With Sickle Cell Disease in Low-Prevalence, High-Income Countries: Qualitative Exploration of Patient Requirements

Background

Sickle cell disease (SCD) is a hematological genetic disease affecting over 25 million people worldwide. The main clinical manifestations of SCD, hemolytic anemia and vaso-occlusion, lead to chronic pain and organ damages. With recent advances in childhood care, high-income countries have seen SCD drift from a disease of early childhood mortality to a neglected chronic disease of adulthood. In particular, coordinated, preventive, and comprehensive care for adults with SCD is largely underresourced. Consequently, patients are left to self-manage. Mobile health (mHealth) apps for chronic disease self-management are now flooding app stores. However, evidence remains unclear about their effectiveness, and the literature indicates low user engagement and poor adoption rates. Finally, few apps have been developed for people with SCD and none encompasses their numerous and complex self-care management needs.

Objective

This study aimed to identify factors that may influence the long-term engagement and user adoption of mHealth among the particularly isolated community of adult patients with SCD living in low-prevalence, high-income countries.

Methods

Semistructured interviews were conducted. Interviews were audiotaped, transcribed verbatim, and analyzed using thematic analysis. Analysis was informed by the Braun and Clarke framework and mapped to the COM-B model (capability, opportunity, motivation, and behavior). Results were classified into high-level functional requirements (FRs) and nonfunctional requirements (NFRs) to guide the development of future mHealth interventions.

Results

Overall, 6 males and 4 females were interviewed (aged between 21 and 55 years). Thirty FRs and 31 NFRs were extracted from the analysis. Most participants (8/10) were concerned about increasing their physical capabilities being able to stop pain symptoms quickly. Regarding the psychological capability aspects, all interviewees desired to receive trustworthy feedback on their self-care management practices. About their physical opportunities, most (7/10) expressed a strong desire to receive alerts when they would reach their own physiological limitations (ie, during physical activity). Concerning social opportunity, most (9/10) reported wanting to learn about the self-care practices of other patients. Relating to motivational aspects, many interviewees (6/10) stressed their need to learn how to avoid the symptoms and live as normal a life as possible. Finally, NFRs included inconspicuousness and customizability of user experience, automatic data collection, data shareability, and data privacy.

Conclusions

Our findings suggest that motivation and engagement with mHealth technologies among the studied population could be increased by providing features that clearly benefit them. Self-management support and self-care decision aid are patients’ major demands. As the complexity of SCD self-management requires a high cognitive load, pervasive health technologies such as wearable sensors, implantable devices, or inconspicuous conversational user interfaces should be explored to ease it. Some of the required technologies already exist but must be integrated, bundled, adapted, or improved to meet the specific needs of people with SCD.

Optical Sensor for Real-Time pH Monitoring in Human Tissue

This article reports on a fiber-based ratiometric optical pH sensor for use in real-time and continuous in vivo pH monitoring in human tissue. Stable hybrid sol-gel-based pH sensing material is deposited on a highly flexible plastic optical fiber tip and integrated with excitation and detection electronics. The sensor is extensively tested in a laboratory environment before it is applied in vivo in a human model. The pH sensor performance in the laboratory environment outperforms the state-of-the-art reported in the current literature. It exhibits the highest sensitivity in the physiological pH range, resolution of 0.0013 pH units, excellent sensor to sensor reproducibility, long-term stability, short response time of <2 min, and drift of 0.003 pH units per 22 h. The sensor also exhibits promising performance in in vitro whole blood samples. In addition, human evaluations conducted under this project demonstrate successful short-term deployment of this sensor in vivo.

Ultrasonic frequency analysis for estimating pH in albumin-rich biofluids

Ultrasound is known as a non-invasive imaging modality capable of propagating through highly scattering media such as tissue, blood, and other biological fluids, yet currently provides little chemical information. We have developed a straightforward and rapid methodology for estimating pH in albumin-rich biofluids based on analysis of ultrasonic frequencies. Albumin is the most abundant protein in serum and undergoes conformational changes with pH. It was shown that when ultrasound propagated through albumin solutions, the attenuation of collected ultrasound signals increased with pH. By measuring the ultrasound frequency spectra at several albumin concentrations and pH values, the pH of the solutions could be determined by multilinear regression. Differences in absolute protein content contributed to signal differences in the frequency profiles and were minimized through normalization of each spectrum by the sum of all its frequency intensities. This strategy was applied to human serum samples from multiple donors, for which a multilinear regression model was developed with a coefficient of determination (R(2)) of 0.93 and a standard error of estimate (SEE) of 0.08 pH units. The use of albumin as a pH indicator opens the doors for estimations in other albumin-rich media, such as amniotic fluid and cerebrospinal fluid.

Facile preparation of biocompatible and robust fluorescent polymeric nanoparticles via PEGylation and cross-linking

Novel cross-linked copolymers of PEG-IM-PhNH2 are successfully synthesized through PEGylation via radical polymerization of 2-isocyanatoethyl methacrylate and poly(ethylene glycol) monomethyl ether methacylate and subsequent cross-linking with an amino-terminated aggregation-induced emission fluorogen. Such obtained amphiphilic copolymers can self-assemble to form uniform fluorescent polymeric nanoparticles (FPNs) and be utilized for cell imaging. These cross-linked FPNs are demonstrated good water dispersibility with ultralow critical micelle concentration (∼ 0.002 mg mL(-1)), uniform morphology (98 ± 2 nm), high red fluorescence quantum yield, and excellent biocompatibility. More importantly, this novel strategy of fabricating cross-linked FPNs paves the way to the future development of more robust and biocompatible fluorescent bioprobes.

Fluorescent polymeric nanoparticles with ultra-low CMC for cell imaging

Fluorescent polymeric nanoparticles (FPNs) with ultra-low critical micelle concentration were facilely fabricated through radical polymerization and ring-opening crosslinking, and utilized for cell imaging.

Double-pass Mach-Zehnder fiber interferometer pH sensor

A biocompatible fiber-optic pH sensor based on a unique double-pass Mach-Zehnder interferometer is proposed. pH responsive poly(2-hydroxyethyl methacrylate-co-2-(dimethylamino)ethyl methacrylate) hydrogel coating on the fiber swells/deswells in response to local pH, leading to refractive index changes that manifest as shifting of interference dips in the optical spectrum. The pH sensor is tested in spiked phosphate buffer saline and demonstrates high sensitivity of 1.71  nm/pH, pH 0.004 limit of detection with good responsiveness, repeatability, and stability. The proposed sensor has been successfully applied in monitoring the media pH in cell culture experiments to investigate the relationship between pH and cancer cell growth.