Automated assessment of mental workload from PPG sensor data using cross-wavelet coherence and transfer learning.

Highly complex cognitive works require more brain power. The productivity of a person suffers due to this strain, which is sometimes referred to as a mental burden or psychological load. A person's mental health and safety in high-stress working conditions can be improved with the help of mental workload assessment. A photoplethysmogram (PPG) signal is a non-invasive and easily acquired physiological signal that contains information related to blood volume changes in the micro-vascular bed of tissues and can indicate psychologically relevant information to assess a person's mental workload (MW). An individual under a high MW possesses an increase in sympathetic nervous system activity, which results in morphological changes in the PPG waveform. In this work, a time-frequency analysis framework is developed to capture these distinguishing PPG features for the automatic assessment of MW. In particular, a cross-wavelet coherence (WTC) approach is proposed to extract simultaneous time-frequency information of the PPG during MW relative to the resting PPG. The suggested technique is validated on a publicly available data set of 22 healthy individuals who took part in an N-back task with PPG recording. Under three different fixed window lengths, images are obtained using WTC between PPG records during N-back task activity and rest. The images are used further to obtain PPG classification in two broad classes of low and high MW using a customized pre-trained Inception-V3 model. The best validation and test accuracy of 93.86% and 93.07%, respectively obtained in the window setting of 1200 samples used for WTC image creation.

CIsense: an automated framework for early screening of cerebral infarction using PPG sensor data.

A cerebral infarction (CI), often known as a stroke, is a cognitive impairment in which a group of brain cells perishes from a lack of blood supply. The early prediction and evaluation of this problem are essential to avoid atrial fibrillation, heart valve disease, and other cardiac disorders. Different clinical strategies like Computerized tomography (CT) scans, Magnetic resonance imaging (MRI), and Carotid (ka-ROT-id) ultrasound are available to diagnose this problem. However, these methods are time-consuming and expensive. Wearable devices based on photoplethysmography (PPG) are gaining prevalence in diagnosing various cardiovascular diseases. This work uses the PPG signal to classify the CI subjects from the normal. We propose an automated framework and fiducial point-independent approach to predict CI with sufficient accuracy. The experiment is performed with a publicly available database having PPG and other physiological data of 219 individuals. The best validation and test accuracy of 91.8% and 91.3% are obtained after diagnosis with Coarse Gaussian SVM. The proposed work aims to extract cerebral infarction pathology by extracting relevant entropy features from higher order PPG derivatives for the prediction of CI and offers a simple, automated and inexpensive approach for early detection of CI and promotes awareness for the subjects to undergo further treatment to avoid major disorders.

Transition from Dion-Jacobson hybrid layered double perovskites to 1D perovskites for ultraviolet to visible photodetection.

New perovskite phases having diverse optoelectronic properties are the need of the hour. We present five variations of R2AgM(iii)X8, where R = NH3C4H8NH3 (4N4) or NH3C6H12NH3 (6N6); M(iii) = Bi3+ or Sb3+; and X = Br- or I-, by tuning the composition of (4N4)2AgBiBr8, a structurally rich hybrid layered double perovskite (HLDP). (4N4)2AgBiBr8, (4N4)2AgSbBr8, and (6N6)2AgBiBr8 crystallize as Dion-Jacobson (DJ) HLDPs, whereas 1D (6N6)SbBr5, (4N4)-BiI and (4N4)-SbI have trans-connected chains by corner-shared octahedra. Ag+ stays out of the 1D lattice either when SbBr63- distortion is high or if Ag+ needs to octahedrally coordinate with I-. Band structure calculations show a direct bandgap for all the bromide phases except (6N6)2AgBiBr8. (4N4)2AgBiBr8 with lower octahedral tilt shows a maximum UV responsivity of 18.8 ± 0.2 A W-1 and external quantum efficiency (EQE) of 6360 ± 58%, at 2.5 V. When self-powered (0 V), (4N4)-SbI has the best responsivity of 11.7 ± 0.2 mA W-1 under 485 nm visible light, with fast photoresponse ≤100 ms.

Multimodal Biofilm Inactivation Using a Photocatalytic Bismuth Perovskite-TiO2-Ru(II)polypyridyl-Based Multisite Heterojunction.

Infectious bacterial biofilms are recalcitrant to most antibiotics compared to their planktonic version, and the lack of appropriate therapeutic strategies for mitigating them poses a serious threat to clinical treatment. A ternary heterojunction material derived from a Bi-based perovskite-TiO2 hybrid and a [Ru(2,2'-bpy)2(4,4'-dicarboxy-2,2'-bpy)]2+ (2,2'-bpy, 2,2'-bipyridyl) as a photosensitizer (RuPS) is developed. This hybrid material is found to be capable of generating reactive oxygen species (ROS)/reactive nitrogen species (RNS) upon solar light irradiation. The aligned band edges and effective exciton dynamics between multisite heterojunctions are established by steady-state/time-resolved optical and other spectroscopic studies. Proposed mechanistic pathways for the photocatalytic generation of ROS/RNS are rationalized based on a cascade-redox processes arising from three catalytic centers. These ROS/RNS are utilized to demonstrate a proof-of-concept in treating two elusive bacterial biofilms while maintaining a high level of biocompatibility (IC50 > 1 mg/mL). The in situ generation of radical species (ROS/RNS) upon photoirradiation is established with EPR spectroscopic measurements and colorimetric assays. Experimental results showed improved efficacy toward biofilm inactivation of the ternary heterojunction material as compared to their individual/binary counterparts under solar light irradiation. The multisite heterojunction formation helped with better exciton delocalization for an efficient catalytic biofilm inactivation. This was rationalized based on the favorable exciton dissociation followed by the onset of multiple oxidation and reduction sites in the ternary heterojunction. This together with exceptional photoelectric features of lead-free halide perovskites outlines a proof-of-principle demonstration in biomedical optoelectronics addressing multimodal antibiofilm/antimicrobial modality.

Exploiting moving slope features of PPG derivatives for estimation of mean arterial pressure.

Monitoring Mean Arterial Pressure (MAP) helps calculate the arteries' flow, resistance, and pressure. It allows doctors to check how well the blood flows through our body and reaches all major organs. Photoplethysmogram technology is gaining momentum and popularity in smart wearable devices to monitor cuff-less blood pressure (BP). However, the performance reliability of the existing PPG-based BP estimation devices is still poor. Inaccuracy in estimating systolic and diastolic blood pressure leads to an overall imprecision in resultant MAP values. Hence, there is a need for robust and reliable MAP estimation algorithms. This work exploits the moving slope features of PPG contour in its first and second derivatives that directly correlate with MAP and does not require estimating systolic and diastolic blood pressure values. The proposed approach is evaluated using two different data sets (i.e., MIMIC-I and MIMIC-II) to demonstrate the robustness and reliability of the work for personalized non-invasive BP monitoring devices to estimate MAP directly. A mean absolute error of 1.28 mmHg and a standard deviation of 2.50 mmHg is obtained with MIMIC-II data-set using GridSearchCV random forest regressor that outperformed most of the existing related works.

Modulating Resonance Energy Transfer with Supramolecular Control in a Layered Hybrid Perovskite and Chromium Photosensitizer Assembly.

Recently, the low-dimensional organic-inorganic halide perovskites (OIHP) have been exploited heavily for their favorable exciton dynamics, broad-band emission, remarkable stability, and tunable band-edge excited-state energy compared to their 3D counterparts for potential optoelectronic applications. Low-dimensional perovskites are generally good candidates for utilization as room-temperature photoluminescence (PL) materials. Further, doping divalent transition metals like Mn2+ into OIHP is expected to introduce a 4T1-6A1-based low-energy luminescence emission around 600 nm; an optical property that is favorable for biomedical optoelectronics. Doping Mn2+ in the perovskite lattice is also expected to induce the generation of cytotoxic singlet oxygen species (1O2), a ROS that is being exploited for various therapeutic applications. To integrate these optical and therapeutic properties of a 2D (PEA)2PbBr4 (Pb PeV; PEA = phenylethylammonium cation) perovskite alloyed with Mn2+ ions (Mn:PbPeV) and the option for a photoinduced energy transfer process involving a Cr(III)-based 1O2 generating photosensitizer (CrPS), we designed a unique purpose-built nanoassembly (Mn:PbPeV@PCD) using the encapsulation properties of a water-soluble polymer derived from ß-cyclodextrin (PCD). Here the PCD is observed to modulate the classical internal energy transfer of Pb2+ exciton to alloyed Mn2+ orange emission, resulting in the emergence of a new blue emission. The addition of CrPS into the Mn:PbPeV@PCD to generate the CrPS@Mn:PbPeV@PCD assembly results in restoring perovskite luminescence followed by the external energy transfer to CrPS. We have elucidated the mechanism of these cascade energy transfer processes between multiple components using steady-state and time-resolved luminescence techniques. Efficient ROS generation and its potential to induce an oxidation reaction of a biomolecule are realized using guanine as the target molecule. Further photoinduced cleavage studies with biomolecules confirmed the efficacy of the nanoassembly in inducing the cleavage of guanine-rich DNA. The study opens up a new direction in the field of perovskite for biomedical applications.

Spacer Switched Two-Dimensional Tin Bromide Perovskites Leading to Ambient-Stable Near-Unity Photoluminescence Quantum Yield.

Semiconductor nanostructures with near-unity photoluminescence quantum yields (PLQYs) are imperative for light-emitting diodes and display devices. A PLQY of 99.7 ± 0.3% has been obtained by stabilizing 91% Sn2+ in the Dion-Jacobson (8N8)SnBr4 (8N8-DJ) perovskite with 1,8-diaminooctane (8N8) spacer. The PLQY is favored by a longer spacer molecule and out-of-plane octahedral tilting. The PLQY shows one-month ambient stability under high relative humidity (RH) and temperature. With n-octylamine (8N) spacer, Ruddlesden-Popper (8N)2SnBr4 (8N-RP) also shows PLQY of 91.7 ± 0.6%, but it has poor ambient stability. The 5-300 K PL experiments decipher the self-trapped excitons (STEs) where the self-trapping depth is 25.6 ± 0.4 meV below the conduction band because of strong carrier-phonon coupling. The microsecond long-lived STE dominates over the band edge (BE) peaks at lower excitation wavelengths and higher temperatures. The higher PLQY and stability of 8N8-DJ are due to the stronger interaction between SnBr64- octahedra and 8N8 spacer, leading to a rigid structure.

Energy-Based DCT Approach for PPG Compression.

With the rapid development of communications, information technology, and Internet of Things (IoT), photoplethysmography (PPG) has achieved prevalence in telemedicine and remote health monitoring using wearable devices. As these devices are resource-constrained, efficient compression techniques are necessary for optimal storage and power consumption management with sustained clinical morphology of PPG signal. This work presents a new approach for PPG compression based on the energy of discrete cosine transform (DCT). With better data compression, a significant reduction of noise is also obtained in the reconstructed signal. The performance evaluation is done on multiple publicly available databases, an average compression ratio of 37.46 is achieved on MIMIC-II database with percentage root-mean-square difference of 0.0688, which is significantly higher than the existing PPG-compression approaches in the literature. Clinical relevance- The work is intended to promote the integration of this combined compression and denoising algorithm for PPG-based devices. The approach is helpful to impart optimization of memory and preserve the clinically relevant information of PPG signals in terms of its useful fiducial points. Further it can amplify ubiquitous computing health monitoring with faster diagnosis and feedback.