Eco-Friendly Cerium-Cobalt Counter-Doped Bi2Se3 Nanoparticulate Semiconductor: Synergistic Doping Effect for Enhanced Thermoelectric Generation.

Metal chalcogenides are primarily used for thermoelectric applications due to their enormous potential to convert waste heat into valuable energy. Several studies focused on single or dual aliovalent doping techniques to enhance thermoelectric properties in semiconductor materials; however, these dopants enhance one property while deteriorating others due to the interdependency of these properties or may render the host material toxic. Therefore, a strategic doping approach is vital to harness the full potential of doping to improve the efficiency of thermoelectric generation while restoring the base material eco-friendly. Here, we report a well-designed counter-doped eco-friendly nanomaterial system (~70 nm) using both isovalent (cerium) and aliovalent (cobalt) in a Bi2Se3 system for enhancing energy conversion efficiency. Substituting cerium for bismuth simultaneously enhances the Seebeck coefficient and electrical conductivity via ionized impurity minimization. The boost in the average electronegativity offered by the self-doped transitional metal cobalt leads to an improvement in the degree of delocalization of the valence electrons. Hence, the new energy state around the Fermi energy serving as electron feed to the conduction band coherently improves the density of the state of conducting electrons. The resulting high power factor and low thermal conductivity contributed to the remarkable improvement in the figure of merit (zT = 0.55) at 473 K for an optimized doping concentration of 0.01 at. %. sample, and a significant nanoparticle size reduction from 400 nm to ~70 nm, making the highly performing materials in this study (Bi2-xCexCo2x3Se3) an excellent thermoelectric generator. The results presented here are higher than several Bi2Se3-based materials already reported.

Investigation on the Direct and Bystander Effects in HeLa Cells Exposed to Very Low α-Radiation Using Electrical Impedance Measurement.

The impact of radiation-induced bystander effect (RIBE) is still not well understood in radiotherapy. RIBEs are biological effects expressed by nonirradiated cells near or far from the irradiated cells. Most radiological studies on cancer cells have been based on biochemical characterization. However, biophysical investigation with label-free techniques to analyze and compare the direct irradiation effect and RIBE has lagged. In this work, we employed an electrical cell-indium tin oxide (ITO) substrate impedance system (ECIIS) as a bioimpedance sensor to evaluate the HeLa cells' response. The bioimpedance of untreated/nonirradiated HeLa (N-HeLa) cells, α-particle (Am-241)-irradiated HeLa (I-HeLa) cells, and bystander HeLa (B-HeLa) cells exposed to media from I-HeLa cells was monitored with a sampling interval of 8 s over a period of 24 h. Also, we imaged the cells at times where impedance changes were observed. Different radiation doses (0.5 cGy, 1.2 cGy, and 1.7 cGy) were used to investigate I-HeLa and B-HeLa cells' radiation-dose-dependence. By analyzing the changes in absolute impedance and cell size/number with time, compared to N-HeLa cells, B-HeLa cells mimicked the I-HeLa cells' damage and modification of proliferation rate. Contrary to the irradiated cells, the bystander cells' damage rate and proliferation rate enhancements have an inverse radiation-dose-response. Also, we report multiple RIBEs in HeLa cells in a single measurement and provide crucial insights into the RIBE mechanism without any labeling procedure. Unambiguously, our results have shown that the time-dependent control of RIBE is important during α-radiation-based radiotherapy of HeLa cells.

Development of a carboxyl-terminated indium tin oxide electrode for improving cell adhesion and facilitating low noise, real-time impedance measurements.

The working electrode's surface property is crucial to cell adhesion and signal collection in electric cell-substrate impedance sensing (ECIS). To date, the indium tin oxide (ITO)-based working electrode is of interest in ECIS study due to its high transparency and biocompatibility. Of great concern is the impedance signal loss, distortion, and data interpretation conflict profoundly created by the movement of multiple cells during ECIS study. Here, a carboxyl-terminated ITO substrate was prepared by stepwise surface amino silanization, with N-hydroxy succinimide (NHS) and 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) treatment, respectively. We investigated the stepwise changes in the property of the treated ITO, cell-substrate adhesion, collective cell mobility, and time course of change in absolute impedance from multiple Chinese hamster ovary (CHO) cells [(Δt-Δ|Z|)CELLS]. The carboxyl-terminated ITO substrate with a surface roughness of 6.37 nm shows enhanced conductivity, 75% visible light transparency, improved cell adherence, reduced collective cell migration speed by approximately twofold, and diminished signal distortion in the [(Δt-Δ|Z|)CELLS]. Thus, our study provides an ITO surface-treatment strategy to reduce multiple cell movement effects and to obtain essential cell information from the ECIS study of multiple cells through undistorted (Δt-Δ|Z|)CELLS.

CHO cell dysfunction due to radiation-induced bystander signals observed by real-time electrical impedance measurement.

Radiation-induced bystander effects (RIBE) have raised many concerns about radiation safety and protection. In RIBE, unirradiated cells receive signals from irradiated cells and exhibit irradiation effects. Until now, most RIBE studies have been based on morphological and biochemical characterization. However, research on the impact of RIBE on biophysical properties of cells has been lagging. Non-invasive indium tin oxide (ITO)-based impedance systems have been used as bioimpedance sensors for monitoring cell behaviors. This powerful technique has not been applied to RIBE research. In this work, we employed an electrical cell-ITO substrate impedance system (ECIIS) to study the RIBE on Chinese hamster ovary (CHO) cells. The bioimpedance of bystander CHO cells (BCHO), alpha(α)-particle (Am-241) irradiated CHO (ICHO), and untreated/unirradiated CHO (UCHO) cells were monitored with a sampling interval of 8 s over a period of 24 h. Media from ICHO cells exposed to different radiation doses (0.3 nGy, 0.5 nGy, and 0.7 nGy) were used to investigate the radiation dose dependence of BCHO cells' impedance. In parallel, we imaged the cells at times where impedance changes were observed. By analyzing the changes in absolute impedance and cell size/cell number with time, we observed that BCHO cells mimicked ICHO cells in terms of modification in cell morphology and proliferation rate. Furthermore, these effects appeared to be time-dependent and inversely proportional to the radiation dose. Hence, this approach allows a label-free study of cellular responses to RIBE with high sensitivity and temporal resolution and can provide crucial insights into the RIBE mechanism.

Simultaneous Enhancement of Thermopower and Electrical Conductivity through Isovalent Substitution of Cerium in Bismuth Selenide Thermoelectric Materials.

It is challenging to achieve highly efficient thermoelectric materials due to the conflicts between thermopower (Seebeck coefficient) and electrical conductivity. These parameters are the core factors defining the thermoelectric property of any material. Here, we report the use of isovalent substitution as a tool to decouple the interdependency of the Seebeck coefficient and the electrical properties of cerium-doped bismuth selenide thermoelectric material. With this strategy, we can achieve a simultaneous increase in both the electrical conductivity and the Seebeck coefficient of the material by tuning the concentration of cerium doping, due to formation of neutral impurities and consequently the improvement of carrier mobility. Our theoretical calculation reveals a downward shift of the valence band with cerium concentration, which influences the thermoelectric enhancement of the synthesized materials. Finally, an order of magnitude enhancement of the figure of merit is obtained due to isovalent substitution, thus providing a new avenue for enhancing the thermoelectric performance of materials.