Multiscale photoacoustic tomography using reversibly switchable thermochromics.

Significance: Based on acoustic detection of optical absorption, photoacoustic tomography (PAT) allows functional and molecular imaging beyond the optical diffusion limit with high spatial resolution. However, multispectral functional and molecular PAT is often limited by decreased spectroscopic accuracy and reduced detection sensitivity in deep tissues, mainly due to wavelength-dependent optical attenuation and inaccurate acoustic inversion. Aim: Previous work has demonstrated that reversible color-shifting can drastically improve the detection sensitivity of PAT by suppressing nonswitching background signals. We aim to develop a new color switching-based PAT method using reversibly switchable thermochromics (ReST). Approach: We developed a family of ReST with excellent water dispersion, biostability, and temperature-controlled color changes by surface modification of commercial thermochromic microcapsules with the hydrophilic polysaccharide alginate. Results: The optical absorbance of the ReST was switched on and off repeatedly by modulating the surrounding temperature, allowing differential photoacoustic detection that effectively suppressed the nonswitching background signal and substantially improved image contrast and detection sensitivity. We demonstrate reversible thermal-switching imaging of ReST in vitro and in vivo using three PAT modes at different length scales. Conclusions: ReST-enabled PAT is a promising technology for high-sensitivity deep tissue imaging of molecular activity in temperature-related biomedical applications, such as cancer thermotherapy.

High-Energy-Density Organic Amendments Enhance Soil Health.

Soil microbial biomass (SMB) and soil microbial communities (SMCs) are the key factors in soil health and agricultural sustainability. We hypothesized that low bioavailable carbon (C) and energy were the key limiting factors influencing soil microbial growth and developed a new fertilization system to address this: the simultaneous application of mineral fertilizers and high-energy-density organic amendments (HED-OAs). A microcosm soil incubation experiment and a Brassica rapa subsp. chinensis pot culture experiment were used to test the effects of this new system. Compared to mineral fertilizer application alone, the simultaneous input of fertilizers and vegetable oil (SIFVO) achieved a bacterial abundance, fungal abundance, and fungal:bacterial ratio that were two orders of magnitude higher, significantly higher organic C and nitrogen (N) content, significantly lower N loss, and nearly net-zero N2O emissions. We proposed an energy and nutrient threshold theory to explain the observed bacterial and fungal growth characteristics, challenging the previously established C:N ratio determination theory. Furthermore, SIFVO led to microbial community improvements (an increased fungal:bacterial ratio, enriched rhizosphere bacteria and fungi, and reduced N-transformation bacteria) that were beneficial for agricultural sustainability. A low vegetable oil rate (5 g/kg) significantly promoted Brassica rapa subsp. chinensis growth and decreased the shoot N content by 35%, while a high rate caused severe N deficiency and significantly inhibited growth of the crop, confirming the exceptionally high microbial abundance and indicating severe microbe-crop competition for nutrients in the soil.

Ultrahigh Frequency Ultrasonic Transducers Design with Low Noise Amplifier Integrated Circuit.

This paper describes the design of an ultrahigh frequency ultrasound system combined with tightly focused 500 MHz ultrasonic transducers and high frequency wideband low noise amplifier (LNA) integrated circuit (IC) model design. The ultrasonic transducers are designed using Aluminum nitride (AlN) piezoelectric thin film as the piezoelectric element and using silicon lens for focusing. The fabrication and characterization of silicon lens was presented in detail. Finite element simulation was used for transducer design and evaluation. A custom designed LNA circuit is presented for amplifying the ultrasound echo signal with low noise. A Common-source and Common-gate (CS-CG) combination structure with active feedback is adopted for the LNA design so that high gain and wideband performances can be achieved simultaneously. Noise and distortion cancelation mechanisms are also employed in this work to improve the noise figure (NF) and linearity. Designed by using a 0.35 µm complementary metal oxide semiconductor (CMOS) technology, the simulated power gain of the echo signal wideband amplifier is 22.5 dB at 500 MHz with a capacitance load of 1.0 pF. The simulated NF at 500 MHz is 3.62 dB.

Potential utilization of waste sweetpotato vines hydrolysate as a new source for single cell oils production by Trichosporon fermentans.

The enzymatic hydrolysate of sweetpotato vines (SVH) characterized as an effective nutrients supplier with low nitrogen availability was firstly used as a substrate by Trichosporon fermentans for single cell oils (SCOs) production. Batch-fermentation experiments on various SVH based media suggested that co-fermentation of SVH and some high-sugar content substrates would be much more efficient and less-cost for SCOs production. A lipid yield of 9.6 g l(-1) with a lipid content of 35.6% was achieved on the SVH without any addition, while 27.6 and 17.7 g l(-1) lipid were respectively obtained on the fructose supplemented SVH media and the SVH mixed with acid treated wheat straw hydrolysate (WSH). The positive effect of SVH on the lipid production of T. fermentans was further demonstrated with a kinetic investigation revealing that SVH had a remarkable promoting effect on the biomass formation and the substrate uptake.

Alumina/epoxy nanocomposite matching layers for high-frequency ultrasound transducer application.

Mismatch of acoustic impedance at the interface between a piezoelectric transducer and the medium to be probed will substantially reduce the amount of ultrasound energy being transmitted into the medium. Therefore, matching layer is a critical component of an ultrasonic transducer. A spin-coating process was used to fabricate alumina/polymer nanocomposite films with alumina volume fractions ranging from 14 to 32%. The particle size of alumina is in the range of 10 to 40 nm. The thicknesses of the matching layer can be controlled by the spinning speed and the concentration of solution. Acoustic impedances of these nanocomposite matching layers are in the range of 2.8 to 5.1 MRayls with different alumina contents, which meet the matching layer requirement. The attenuation of a nanocomposite matching layer with smooth surface is about 15 dB/mm at 40 MHz. The pulse-echo spectrum and frequency spectrum of a high-frequency transducer using this nanocomposite matching layer are reported.

Acoustic properties of alumina colloidal/polymer nano-composite film on silicon.

Alumina colloidal/polymer composite films on silicon substrates have been successfully fabricated using the sol-gel method, in which the crystallite sizes of alumina are between 20 and 50 nm. The density and ultrasonic phase velocities in these films with different alumina ratios from 14% to 32% were measured at the desired operating frequency. We have proved that the density, acoustic phase velocities, and hence the acoustic impedance of the nano-composite films increase with the alumina content, which gives us another option of tailoring the acoustic impedance of the nano-composite film for making the matching layer of high-frequency medical ultrasonic transducers.