Copper Catalysis-Based Amperometric Microsensors for Carbon Dioxide Monitoring.

A fast response microsensor that can detect the distribution of CO2 at the microscale level is essential for the observation of biophysiological activity, carbon flux, and carbon burial. Inspired by the previous success of Cu catalysis, we attempted to use this metal Cu material to develop an amperometric microsensor that can meet the requirements. Specifically, the ambient gases diffuse through a silicone membrane into a trap casing filled with an acidic CrCl2 solution, where the otherwise interfering O2 interferent is removed by a redox with Cr2+. The gases then diffuse through a second silicone membrane into an electrolyte, where CO2 is selectively reduced to methanol (CH3OH) at a Cu cathode through a carbon monoxide (CO) pathway. Due to the use of Cu catalysis at the WE tip, CO2 can be reduced at a less negative polarization (-470 mV) instead of the previously reported -1200 mV, thus avoiding hydrogen-evolution interference due to water from the byproduct or from water diffusion through the silicone membrane. This moderate polarization results in a stable baseline, making the microsensor suitable for long-term monitoring. Interferences from other gases, such as N2O, which may be of much concern in environmental monitoring, can be ignored. Applications and limitations are also discussed with a view to further improvement in the future.

Three-dimensional polarization effects in optical tunneling.

We consider the three-dimensional (3D) polarimetric properties of an evanescent optical field excited in the gap of a double-prism system by a random plane wave. The analysis covers the case of frustrated total internal reflection (FTIR), i.e., optical tunneling, and relies on the characteristic decomposition of the 3×3 polarization matrix. We find in particular that, for any incident partially polarized plane wave, the evanescent field inside the gap is necessarily in a nonregular, genuine 3D polarization state. We also show that the 3D polarimetric properties of the field at the second boundary are sensitive to the changes of the gap width and that the relevant effects occur for the smaller widths when the angle of incidence of the plane wave becomes larger. The results of this work uncover new aspects of the polarimetric structure of genuine 3D evanescent fields and may find applications in near-field optics and surface nanophotonics.

Delivery of Doxorubicin by Ferric Ion-Modified Mesoporous Polydopamine Nanoparticles and Anticancer Activity against HCT-116 Cells In Vitro.

In clinical cancer research, photothermal therapy is one of the most effective ways to increase sensitivity to chemotherapy. Here, we present a simple and effective method for developing a nanotherapeutic agent for chemotherapy combined with photothermal therapy. The nanotherapeutic agent mesoporous polydopamine-Fe(III)-doxorubicin-hyaluronic acid (MPDA-Fe(III)-DOX-HA) was composed of mesoporous polydopamine modified by ferric ions and loaded with the anticancer drug doxorubicin (DOX), as well as an outer layer coating of hyaluronic acid. The pore size of the mesoporous polydopamine was larger than that of the common polydopamine nanoparticles, and the particle size of MPDA-Fe(III)-DOX-HA nanoparticles was 179 ± 19 nm. With the presence of ferric ions, the heat generation effect of the MPDA-Fe(III)-DOX-HA nanoparticles in the near-infrared light at 808 nm was enhanced. In addition, the experimental findings revealed that the active targeting of hyaluronic acid to tumor cells mitigated the toxicity of DOX on normal cells. Furthermore, under 808 nm illumination, the MPDA-Fe(III)-DOX-HA nanoparticles demonstrated potent cytotoxicity to HCT-116 cells, indicating a good anti-tumor effect in vitro. Therefore, the system developed in this work merits further investigation as a potential nanotherapeutic platform for photothermal treatment of cancer.

Highly Selective Microsensor for Monitoring Trace Phosphine in the Environment.

Monitoring P flux at the Earth's surface-atmosphere interface has many challenges. Therefore, the development of a technology with high selectivity and high sensitivity to in situ trace PH3 in aquatic or sedimentary environments has become a priority. Herein, an amperometric PH3 microsensor meeting the above conditions is developed. The sensor is equipped with a Au-coated Pt working electrode (WE) and a Pt guard electrode (GE) positioned in an outer glass casing. The WE and GE are polarized at a fixed value of +150 mV with respect to a pseudo-reference electrode. The outer casing is filled with an acid electrolyte solution, and the tip is sealed using a thin silicone membrane. Mixed gases from the environment diffuse through the first layer of the silicone membrane, and the major H2S disruptor is eliminated by a ZnCl2-propylene carbonate trap positioned in the front of the microsensor. Later, the gases diffuse into an electrolytic solution through the second layer of the silicone membrane, and PH3 is selectively oxidized into H3PO4 on the Au-coated Pt WE. This electrochemical oxidation thereby creates a current that is proportional to the concentration of PH3 (>2 nmol·L-1). With the aid of the H2S trap casing and selective catalysis, the effects of other gases on the microsensor can be ignored in terms of environmental monitoring. An example from the sedimentary profile shows that high PH3 accumulations are found 13 mm below the sediment surface.

Probing coherence Stokes parameters of three-component light with nanoscatterers.

We establish a method to determine the spectral coherence Stokes parameters of a random three-component optical field via scattering by two dipolar nanoparticles. We show that measuring the intensity and polarization-state fringes of the scattered far field in three directions allows us to construct all nine coherence Stokes parameters at the dipoles. The method extends current nanoprobe techniques to detection of the spatial coherence of random light with arbitrary three-dimensional polarization structure.

Polarization properties of stochastic electromagnetic beams modulated by a wavefront-folding interferometer.

We consider the field generated by a wavefront-folding interferometer which is illuminated by a stochastic electromagnetic beam. The specular property and anti-specular property are discussed in the vector case. Take electromagnetic Gaussian Schell-model beam as an example, we investigate the spectral density, the spectral degree of coherence, the spectral degree of polarization as well as the state of polarization of the polarized portion of the field on propagation. Results show that the polarization properties including the degree of polarization, the orientation angle and the degree of ellipse can be adjusted by the phase difference of the interferometer and the phase retardation introduced by the prism. The results may be applied in free-space optical communication.

Interfering optical coherence lattices by use of a wavefront-folding interferometer.

We investigate the properties of an interfering optical coherence lattice, which is generated by passing an optical coherence lattice through a wavefront-folding interferometer. Two symmetrical lattices are formed in the far-field. Changing the phase difference between the two optical paths causes the interference pattern, and thus the far-field intensity profile to change. In addition, we have shown that in the non-uniform case, the intensity pattern can also be changed by varying the weight distribution parameter. Our results may be applied in free-space communications and periodic trapping of micro-particles.

Radiation forces on a Rayleigh dielectric sphere produced by highly focused parabolic scaling Bessel beams.

The radiation forces on a Rayleigh dielectric particle induced by a highly focused parabolic scaling Bessel beam (PSBB) are investigated. Numerical results show that the zero-order PSBB can be used to trap a high-index particle at the focus and near the focus by the first-order PSBB. For the low-index particle, it can be guided or confined in the dark core of the nonzero-order PSBB but cannot be stably trapped in this single-beam trap. Further, we analyze the condition of trapping stability. It is found that the lower limit in the particle radius for stable trapping is different for different orders.

Influence of atmospheric turbulence on the properties of specular and antispecular beams.

A class of optical fields with specular or antispecular properties can be generated by a Gaussian Schell-model beam passing through a wavefront-folding interferometer. Based on the generalized diffraction integral formula, an analytical expression for the cross-spectral density function of such fields propagating through non-Kolmogorov atmospheric turbulence is derived. It is revealed that the specular and antispecular properties of the beams always maintain during propagation in free space. However, the specularity and antispecularity properties of the beams become different in atmosphere, since they are quickly destroyed by the atmospheric turbulence.

Changes in radiation forces acting on a Rayleigh dielectric sphere by use of a wavefront-folding interferometer.

We consider a class of fields generated by passing an isotropic Gaussian Schell-model beam through a wavefront-folding interferometer. The output field has various intensity profiles for different phase differences, including the central peak and doughnut shapes. The radiation force on a Rayleigh dielectric particle produced by the highly focused fields is investigated. Numerical results demonstrate that the new fields can be used to trap high-index particles at the focus for the specular case and nearby the focus for the anti-specular case. It is further revealed that the position, the range of particle sizes and the low limit of correlation length for stable trapping could be modulated by adjusting the phase difference.