This study examines the use of a conductive carbon fiber to construct a flexible biosensing platform for monitoring biomarkers in sweat. Cortisol was chosen as a model analyte. Functionalization of the conductive carbon yarn (CCY) with ellipsoidal Fe2O3 has been performed to immobilize the antibodies specific to cortisol. 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-Hydroxysuccinimide (NHS) chemistry has been used to immobilize the antibodies onto the Fe2O3 modified CCY. Crystallinity, structure, morphology, flexibility, surface area, and elemental analysis were studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FE-SEM/EDS) and Brunauer–Emmett–Teller (BET) analysis. Mechanical properties of the fiber such as tensile strength, young’s modulus have also been investigated. Under optimal parameters, the fabric sensor exhibited a good linearity (r2 = 0.998) for wide a linear range from 1 fg to 1 μg with a detection limit of 0.005 fg/mL for the sensitive detection of cortisol. Repeatability, reliability, reproducibility, and anti-interference properties of the current sensor have been investigated. Detection of cortisol levels in human sweat samples has also been investigated and the results were validated with commercial chemiluminescence immunoassay (CLIA) method.

In the present investigation, for the first time, we have performed a thorough study about different functionals and basis sets for linear and nonlinear optical (NLO) properties of para-nitroaniline ([Formula: see text]-NA), which is considered as proto-type NLO molecule, among organic NLO materials. There is a dire need of such data base for [Formula: see text]-NA because many investigators are using such values of [Formula: see text]-NA for comparative analysis. A range of different functionals including HF, BLYP, PW91, PBE, B3LYP, M06, M06-2X, PBE0, BHandHLYP, CAM-B3LYP, LC-BLYP, and B3LYP-D3 are applied in conjugation with several commonly basis sets such as 6-31G*, 6-311G*, 6-311G**, 6-311+G**, cc-pVDZ, and cc-pVTZ. A variety of functional and basis sets combinations are calculated and graphically compared with each other. The calculated total dipole moment for the [Formula: see text]-NA is found to be 6.79[Formula: see text]D which is quite closer to experimentally determined value. The lowest calculated value for linear isotropic polarizability at HF/6-31G* level of theory is [Formula: see text] esu while higher values observed with remaining all methods especially 14% polarizability increases in presence of basis set with diffuse functions and similar trend of variation is also observed in linear anisotropic polarizability. Similarly, the calculated value of frequency dependent second-order polarizability is found to be [Formula: see text] esu at PBE0/6-311+G** level of theory which is quite closer to experimental value of [Formula: see text] esu. A comparison between the calculated and experimental results shows good agreement among geometries, dipole moments and NLO polarizabilities for [Formula: see text]-NA. Moreover, the frontier molecular orbital (FMO) and electron density difference map (EDDM) analysis along with density of state (DOS) plots are also presented to get more physical intuitions into the structure–property relationship and electronic communications between terminal accepter and donor groups through [Formula: see text]-conjugation. The present investigation provides benchmark data including various commonly used functionals and basis sets for the calculation of NLO properties of [Formula: see text]-NA. Thus, the present investigation will put straight several future studies when it comes to comparative NLO study of organic materials.

Wearable sensors are becoming an important tool for healthcare monitoring as they can provide continuous monitoring of clinically important biomarkers released in the biofluids such as sweat, saliva, tears, urine and interstitial fluids (ISF). Development of smart sensing technologies for stress detection in daily life is find applications in various field including healthcare, defence and sports industries. Although different modalities for stress detection are performed in the clinical laboratories, the measurement of hormone release from glands of the endocrine system is receiving wide attention. Cortisol is considered as a biomarker of stress as the levels are spike in response to stressors. Although most of the cortisol released from adrenaline glands bound by corticosteroid-binding globulin (CBG), active form of free cortisol is also appearing in the biofluids (sweat, saliva, urine, tear, and ISF). Electrochemical biosensors, due to their relative small farm factors and sensitivity are focused for developing wearable biosensors for non-invasive monitoring of biochemical markers. Recent technological advancements in the field of electrochemical sensors and material engineering have contributed widely to the growth of new generation wearable point of care (POC) systems that can allow for early diagnosis. Receptor molecules including antibodies, enzyme fragments, molecularly imprinted polymers, and other biomimetic materials have been explored for electrochemical sensing of cortisol. Interfacing of theses sensing strategies into fabrics and flexible wearable patches for sweat cortisol analysis are also attempted. This mini review focuses on development made in the area of cortisol sensors using fabrics and flexible substrates potential for wearable sensor applications. An overview of cortisol secretion in the body and its availability in different biological fluids are also discussed. The issues associated with realizing complete wearable sensor devices are also explored.

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