Near-Infrared Organic Photodetectors toward Skin-Integrated Photoplethysmography-Electrocardiography Multimodal Sensing System

Novel Flexible Organic Photoplethysmogram Sensor for Continuous Cardiovascular Monitoring

A flexible organic photodetector (OPD) has been developed for a flexible organic photoplethysmography sensor (FOPS) designed to monitor vital cardiovascular parameters such as pulse rate, respiratory rate, blood pressure, and pulse rate variability. This device is fabricated on a flexible substrate, utilizing a blend of PCDTBT and PC71BM as the active layer. The FOPS demonstrates excellent absorption properties across the visible spectrum, which is essential for capturing high-quality arterial pulse signals, known as photoplethysmogram (PPG). Optoelectronic characterization revealed a high response time and an impressive on/off current ratio, enabling the accurate detection of microfeatures within the PPG signal. We successfully utilized the device to monitor PPG signals in both reflection and transmission modes, employing green (530 nm) and red (630 nm) light sources, respectively. The recorded PPG signals were further analyzed to measure cardiovascular parameters. The device also demonstrates the ability to measure blood pressure using two techniques: a cuff-based method in conjunction with the oscillometric waveform (OMW) and a cuff-less technique utilizing an artificial neural network approach. These results highlight the FOPS's potential for integration into wearable medical technology, offering continuous, real-time cardiovascular monitoring in a user-friendly and noninvasive manner.

Heterojunction Derived Efficient Charge Separation for High Sensitivity Self-Powered Flexible Photodetectors toward Real-Time Heart Rate Monitoring

Real-time and accurate heart rate monitoring is crucial in the field of disease prevention and early diagnosis. Compared with the conventional rigid heart rate sensors, wearable flexible devices have unique advantages, such as convenient, high comfortable to the skin, and low data extraction errors. Currently, the available flexible electronic devices encounter with large power consumption, low detectivity, and slow response time, restricting their further commercial applications. Herein, flexible self-powered photodetectors (PDs) are developed by the synergistic strategy of engineering CsPbI3:Ho3+@SnS quantum dots (QDs) p-n heterojunctions and doping SnS QDs into spiro-OMeTAD hole transport layer (HTL). The designing CsPbI3:Ho3+@SnS QDs p-n heterojunctions as the photosensitive layer to effectively enhance the built-in field, reduce defect density, and boost the charge separation efficiency. Meanwhile, the high hole mobility and suitable energy band structure of p-type SnS QDs are doped into spiro-OMeTAD HTL, which can improve the hole extraction, and balance electron and hole mobilities. Such flexible self-powered PDs exhibit excellent sensitivity and stability with high responsivity (0.58 A W-1) and detectivity (1.13×1013 Jones), and fast response time (98.8 µs). The flexible self-powered PDs are further integrated with the light-emitting diodes (LEDs) as a photoplethysmography (PPG) system, realizing real-time and accurate heart rate monitoring.

A KNN-based model for non-invasive prediction of hemorrhagic shock severity in prehospital settings: integrating MAP, PBUCO2, PTCO2, and PPV

BACKGROUND

Rapid prehospital assessment of hemorrhagic shock severity is critical for trauma triage and intervention. Current non-invasive single-parameter monitoring shows limited diagnostic reliability. We developed a multi-parameter predictive model integrating mean arterial pressure (MAP), buccal mucosal CO₂ (PBUCO₂), transcutaneous oxygen (PTCO₂), and pulse pressure variation (PPV). using K-nearest neighbors (KNN) algorithm.

METHODS

Forty-five Wistar rats were randomly divided into five groups (n = 9) with different blood loss amounts. MAP, PBUCO2, PTCO2, and PPV measurements were continuously obtained. A multi-parameter shock severity prediction model was established based on the KNN algorithm. Leave-one-out cross-validation was used to determine the value of K. Meanwhile, a prediction model based on the support vector machine (SVM) algorithm was established. The performance of the two prediction models was compared using confusion matrices and receiver operating characteristic (ROC) curve.

RESULTS

When the training vs testing data set ratio is 7:3 or 6:4, and K = 3, the KNN-based model has the best prediction accuracy (94.82% and 93.51%). The confusion matrix and ROC evaluation showed that the overall performance of the KNN-based model is superior to that of the SVM-based model, at all levels of blood loss (F1 = 95.09% and 93.99%, AUC = 1 and 0.97 for the KNN-based model at 7:3 and 6:4 dataset ratio; F1 = 83.84% and 84.86%, AUC = 0.97 and 0.97 for the SVM-based model at 7:3 and 6:4 dataset ratio).

CONCLUSIONS

Using the detection indicators MAP, PBUCO2, PTCO2 and PPV, the KNN-based rat hemorrhagic shock severity prediction model has high accuracy and stability, and demonstrates potential feasibility for severity stratification of hemorrhagic shock in standardized preclinical models, providing a foundation for future clinical validation in prehospital environments.

Intrinsically-Stretchable and Patternable Quantum Dot Color Conversion Layers for Stretchable Displays in Robotic Skin and Wearable Electronics

Stretchable displays are essential components as signal outputs in next-generation stretchable electronics, particularly for robotic skin and wearable device technologies. Intrinsically-stretchable and patternable color conversion layers (CCLs) offer practical solutions for developing full-color stretchable micro-light-emitting diode (LED) displays. However, significant challenges remain in creating stretchable and patternable CCLs without backlight leakage under mechanical deformation. Here, a novel material strategy for stretchable and patternable heavy-metal-free quantum dot (QD) CCLs, potentially useful for robotic skin and wearable electronics is presented. Through a versatile crosslinking technique, uniform and high-concentration QD loading in the elastomeric polydimethylsiloxane matrix without loss of optical properties is achieved. These CCLs demonstrate excellent color conversion capabilities with minimal backlight leakage, even under 50% tensile strain. Additionally, fine-pixel patterning process with resolutions up to 300 pixels per inch is compatible with the QD CCLs, suitable for high-resolution stretchable display applications. The integration of these CCLs with micro-LED displays is also demonstrated, showcasing their use in haptic-responsive robotic skin and wearable healthcare monitoring sensors. This study offers a promising material preparation methodology for stretchable QDs/polymer composites and highlights their potential for advancing flexible and wearable light-emitting devices.

Transfer Learning Enhanced Blood Pressure Monitoring Based on Flexible Optical Pulse Sensing Patch

Blood pressure (BP), a crucial health biomarker, is essential for detecting early indications of cardiovascular disease in routine monitoring and clinical surveillance of inpatients. However, conventional cuff-based BP measurements are limited in providing continuous comfort monitoring. Here, we present an optical pulse sensing patch for BP monitoring, which integrates three units of Gallium Nitride (GaN) optopairs with micronanostructured polydimethylsiloxane films to capture pulse waves. Multipoint pulse signals are transformed into BP and other cardiovascular indicators through machine learning. The transfer learning method is developed to calibrate the machine learning model with few training sets, simplifying the practical implementation. The developed sensing patch holds great potential for long-term, precise BP monitoring, enhancing clinical diagnosis, and management of cardiovascular diseases.

Recent developments in polymer semiconductors with excellent electron transport performances

Benefiting from molecular design and device innovation, electronic devices based on polymer semiconductors have achieved significant developments and gradual commercialization over the past few decades. Most of high-performance polymer semiconductors that have been prepared exhibit p-type performances, and records of their carrier mobilities are constantly being broken through. Although ambipolar and n-type polymers are necessary for constructing p-n heterojunctions and logic circuits, only a few materials show outstanding device performances, which leads to their developments lagging far behind that of p-type analogues. As a consequence, it is extremely significant to summarize polymer semiconductors with excellent electron transport performances. This review focuses on the design considerations and bonding modes between monomers of polymer semiconductors with high electron mobilities. To enhance electron transport performances of polymer semiconductors, the structural modification strategies are described in detail. Subsequently, the electron transport, thermoelectric, mixed ionic-electronic conduction, intrinsically stretchable, photodetection, and spin transport performances of high-electron mobility polymers are discussed from the perspective of molecular engineering. In the end, the challenges and prospects in this research field are presented, which provide valuable guidance for the design of polymer semiconductors with excellent electron transport performances and the exploration of more advanced applications in the future.

Lighting the Path to Precision Healthcare: Advances and Applications of Wearable Photonic Sensors

Recent advancements in wearable photonic sensors have marked a transformative era in healthcare, enabling non-invasive, real-time, portable, and personalized medical monitoring. These sensors leverage the unique properties of light toward high-performance sensing in form factors optimized for real-world use. Their ability to offer solutions to a broad spectrum of medical challenges - from routine health monitoring to managing chronic conditions, inspires a rapidly growing translational market. This review explores the design and development of wearable photonic sensors toward various healthcare applications. The photonic sensing strategies that power these technologies are first presented, alongside a discussion of the factors that define optimal use-cases for each approach. The means by which these mechanisms are integrated into wearable formats are then discussed, with considerations toward material selection for comfort and functionality, component fabrication, and power management. Recent developments in the space are detailed, accounting for both physical and chemical stimuli detection through various non-invasive biofluids. Finally, a comprehensive situational overview identifies critical challenges toward translation, alongside promising solutions. Associated future outlooks detail emerging trends and mechanisms that stand to enable the integration of these technologies into mainstream healthcare practice, toward advancing personalized medicine and improving patient outcomes.

Integration of Functional Materials in Photonic and Optoelectronic Technologies for Advanced Medical Diagnostics

Integrating functional materials with photonic and optoelectronic technologies has revolutionized medical diagnostics, enhancing imaging and sensing capabilities. This review provides a comprehensive overview of recent innovations in functional materials, such as quantum dots, perovskites, plasmonic nanomaterials, and organic semiconductors, which have been instrumental in the development of diagnostic devices characterized by high sensitivity, specificity, and resolution. Their unique optical properties enable real-time monitoring of biological processes, advancing early disease detection and personalized treatment. However, challenges such as material stability, reproducibility, scalability, and environmental sustainability remain critical barriers to their clinical translation. Breakthroughs such as green synthesis, continuous flow production, and advanced surface engineering are addressing these limitations, paving the way for next-generation diagnostic tools. This article highlights the transformative potential of interdisciplinary research in overcoming these challenges and emphasizes the importance of sustainable and scalable strategies for harnessing functional materials in medical diagnostics. The ultimate goal is to inspire further innovation in the field, enabling the creation of practical, cost-effective, and environmentally friendly diagnostic solutions.

Detecting N-Phenyl-2-Naphthylamine, L-Arabinose, D-Mannose, L-Phenylalanine, L-Methionine, and D-Trehalose via Photocurrent Measurement

The concentration of small molecules reflects the normality of physiological processes in the human body, making the development of simple and efficient detection equipment essential. In this work, inspired by a facile strategy in point-of-care detection, two devices were fabricated to detect small molecules via photocurrent measurement. A linear response of the photocurrent against the concentration of the small molecules was found. In the first device, metal ions were introduced into gel substrates made by xanthan gum to enhance photocurrent response. N-phenyl-2-naphthylamine was measured when iron or manganese ions were used. L-Phenylalanine was measured when the gel was modified by samarium, iron, cerium, or ytterbium ions. L-(+)-Arabinose was detected via the gels modified by iron or holmium ions. D-(+)-Mannose was detected when the gel was modified by ytterbium, manganese, chromium, or sodium ions. L-Methionine was detected in the gels modified by samarium, zinc, or chromium ions. The second device was based on a paper sheet. A sugar-like molecule was first synthesized, which was then used to modify the paper. The detection was possible since the photocurrent showed a linear trend against the concentration of D-Trehalose. A linear fit was conducted to derive the sensitivity, whose value was found to be 5542.4. This work offers a novel, simple, and environmentally sustainable platform that is potentially useful in remote areas lacking medical devices.

Ultrathin crystalline silicon-based omnidirectional strain gauges for implantable/wearable characterization of soft tissue biomechanics

Monitoring soft-tissue biomechanics is of interest in biomedical research and clinical treatment of diseases. An important focus is biointegrated strain gauges that track time-dependent mechanics of targeted tissues with deforming surfaces over multidirections. Existing methods provide limited gauge factors, tailored for sensing within specific directions under quasi-static conditions. We present development and applicability of implantable/wearable strain gauges that integrate multiple ultrathin monocrystalline silicon-based sensors aligned with different directions, in stretchable formats for dynamically monitoring direction angle-sensitive strain. We experimentally and computationally establish operational principles, with theoretical systems that enable determination of intensities and direction of applied strains at an omnidirectional scale. Wearable evaluations range from cardiac pulse to intraocular pressure monitoring of eyeballs. The device can evaluate cardiac disorders of myocardial infarction and hypoxia of living rats and locate the pathological orientation associated with infarction, in designs with possibilities as biodegradable implants for stable operation. These findings create clinical significance of the devices for monitoring complex dynamic biomechanics.

All-solution-processed ultraflexible wearable sensor enabled with universal trilayer structure for organic optoelectronic devices

All-solution-processed organic optoelectronic devices can enable the large-scale manufacture of ultrathin wearable electronics with integrated diverse functions. However, the complex multilayer-stacking device structure of organic optoelectronics poses challenges for scalable production. Here, we establish all-solution processes to fabricate a wearable, self-powered photoplethysmogram (PPG) sensor. We achieve comparable performance and improved stability compared to complex reference devices with evaporated electrodes by using a trilayer device structure applicable to organic photovoltaics, photodetectors, and light-emitting diodes. The PPG sensor array based on all-solution-processed organic light-emitting diodes and photodetectors can be fabricated on a large-area ultrathin substrate to achieve long storage stability. We integrate it with a large-area, all-solution-processed organic solar module to realize a self-powered health monitoring system. We fabricate high-throughput wearable electronic devices with complex functions on large-area ultrathin substrates based on organic optoelectronics. Our findings can advance the high-throughput manufacture of ultrathin electronic devices integrating complex functions.