Abstract
Phase-contrast in tapping-mode atomic force microscopy (TM-AFM) results from dynamic tip-surface interaction losses which allow soft and hard nanoscale features to be distinguished. So far, ...phase-contrast in TM-AFM has been interpreted using homogeneous Boltzmann-like loss distributions that ignore fluctuations. Here, we revisit the origin of phase-contrast in TM-AFM by considering the role of fluctuation-driven transitions and heterogeneous loss. At ultra-light tapping amplitudes <3 nm, a unique amplitude dependent two-stage distribution response is revealed, alluding to metastable viscous relaxations that originate from tapping-induced surface perturbations. The elastic and viscous coefficients are also quantitatively estimated from the resulting strain rate at the fixed tapping frequency. The transitional heterogeneous losses emerge as the dominant loss mechanism outweighing homogeneous losses at smaller amplitudes for a soft-material. Analogous fluctuation mediated phase-contrast is also apparent in contact resonance enhanced AFM-IR (infrared), showing promise in decoupling competing thermal loss mechanisms via radiative and non-radiative pathways. Understanding the loss pathways can provide insights on the bio-physical origins of heterogeneities in soft-bio-matter e.g., single cancer cell, tumors, and soft-tissues.
•UV-triggered polymerization of catecholamine materials forming polydopamine and polynorepinephrine to implement organ-on-a-chip (OOC).•UV-light of a standard biosafety cabinet utilized for the ...polymerization of PDMS substrates.•Three different types of OOCs created using this technique:(i)Plasma-bonded, polymer-coated chips,(ii)UV-bonded, polymer-coated chips,(iii)projection coated fluid wall chips.•The UV-light and the catecholamine material together offer a simple yet effective technique for implementing OOC.
Surface modification of microfluidic chips used for making organ-on-a-chip (OOC) applications is often a time-consuming process, involving chip cleaning, ultraviolet (UV)-exposure, and steam sterilization. This work reports developing a simple, rapid, and cost-effective method that can achieve photo-activated polymerization and patterning of catecholamine materials on microfluidic chips in a single step using the UV light present in a standard biosafety cabinet. Polydimethylsiloxane (PDMS) microfluidic devices were filled with monomers of dopamine and norepinephrine, followed by exposure to UV light triggers polymerization of the material, which creates a highly viable surface for OOC applications. We examined the performance of these UV-triggered surface coatings for creating three different kinds of OOCs, where microfluidic chips were bonded and modified in three different ways: i) conventional oxygen plasma bonded microfluidic chips filled with monomer solutions and then exposed to UV to modify the surface (Plasma bonded, polymer-coated); ii) both the fluidic layer and glass substrate were exposed to UV to coat the functional layer and simultaneously allow adhesive proteins to bind the two pieces together (UV-bonded, polymer-coated); and iii) project the UV light through a mask to create fluid wall microfluidic channels on a polydimethylsiloxane (PDMS) substrate (projection coating). Cath.a.differentiated (CAD) cells seeded on UV-exposed polymer-coated surface in the three techniques showed significantly high cell viability, cell adhesion, proliferation, genetic expression, and they retained the functionality compared to uncoated PDMS. The UV-triggered surface modification technique uses a minimalist approach by using less equipment and existing infrastructure, such as a biosafety cabinet, for creating a functional OOC. This novel, simple, low-cost approach to reproducibly generating an organ-on-a-chip will facilitate the wider adoption of this technique.
Display omitted
Enhancing the piezoresistivity of polymer‐derived silicon oxycarbide ceramics (SiOCPDC) is of great interest in the advancement of highly sensitive pressure/load sensor technology for use in harsh ...and extreme working conditions. However, a facile, low cost, and scalable approach to fabricate highly piezoresistive SiOCPDC below 1400 °C still remains a great challenge. Here, the fabrication and enhancement of piezoresistive properties of SiOCPDC reinforced with β‐SiC nanopowders (SiCNP) through masked stereolithography‐based 3D‐printing and subsequent pyrolysis at 1100 °C are demonstrated. The presence of free carbon in SiCNP augments high piezoresistivity in the fabricated SiCNP‐SiOCPDC composites even at lower pyrolysis temperatures. A gauge factor (GF) in the range of 4385–5630 and 6129–8987 with 0.25 and 0.50 wt% of SiCNP, respectively is demonstrated, for an applied pressure range of 0.5–5 MPa at ambient working conditions. The reported GF is significantly higher compared to those of any existing SiOCPDC materials. This rapid and facile fabrication route with significantly enhanced piezoresistive properties makes the 3D‐printed SiCNP‐SiOCPDC composite a promising high‐performance material for the detection of pressure/load in demanding applications. Also, the overall robustness in mechanical properties and load‐bearing capability ensures its long‐term stability and makes it suitable for challenging and severe environment applications.
A highly piezoresistive SiOCPDC filled with SiCNP is developed using mask stereolithography‐based 3D printing technique. The optimized incorporation of SiCNP improves the piezoresistive properties without deteriorating shrinkage, density, and mechanical properties. This rapid and facile fabrication route with significantly enhanced piezoresistive properties makes the 3D‐printed SiCNP‐SiOCPDC composite a promising high‐performance material for the detection of pressure/load in harsh environments.
Abstract Organic photodetectors (OPDs) hold immense promise for optoelectronic applications. Here a zero‐biased, high‐performance organic photodetector employing a 2D organic heterostructure is ...introduced. The structure combines carbon quantum dots (CQDs) with nitrogen self‐doped graphitic carbon nitride (g‐C 3 N 4+ ) and is tested for alternating current (AC) photodetection on an interdigitated electrode platform. The study reveals extraordinary performance driven by the synergistic effects of efficient charge excitation, separation, and emission within the 2D/2D CQD/g‐C 3 N 4 + heterostructure, leveraging mechanisms of photoconduction, photogating, and fluorescence. A unique convergence to similar rise and decay times in the order of 2.9 ms is observed at higher frequencies in the visible (Vis) spectrum. Benchmarking against state‐of‐the‐art OPDs shows ultrahigh specific detectivity (4.60 × 10 18 Jones), ultrahigh responsivity (1.43 × 10 7 A W −1 ), high external quantum efficiency (43 × 10 7 %) at an optical intensity of 3.56 × 10 −4 mW cm −2 and a wavelength of 405 nm while delivering competitive performance at 532 and 635 nm as well. Moreover, a large linear dynamic range of 86–162 dB in the Vis spectrum is obtained. These enhancements promise development of a new generation of OPDs to advance light sensing and imaging applications at high frequency, marking a significant milestone in optoelectronic device engineering.
A method of power transmission is proposed that delivers power through the resonance of a helical receiver with its surrounding stray capacitance. The system operates in a quasi-wireless state where ...power is transferred over a single connection to a surface much larger than the dimensions of the receiver. This ensures high-efficiency energy transfer over large areas without the need of strong coupling electromagnetic fields. Standard power connectors such as tracks, plugs, and cords may be easily replaced with conductive surfaces or objects such as foil sheets, desks, and cabinets. Presently, the method is experimentally demonstrated at the small scale using loads of up to 50 W at an efficiency of 83% with both bare and insulated surfaces. Simple circuit modeling of the system is presented which shows close agreement with experimental results.
Metal–organic frameworks (MOFs) present specific adsorption sites with varying electron affinity which are uniquely conducive to selective gas sensing but are typically large-band-gap insulators. On ...the contrary, multiwall carbon nanotubes (MWCNTs) exhibit superior mesoscopic transport exploiting strong electron correlations among sub-bands below and above the Fermi level at room temperature. We synergize them in a new class of nanocomposites based on zeolitic imidazolate framework-8 (ZIF-8) and report selective sensing of CH4 in ∼10 parts-per-billion (ppb) with a determined limit of detection of ∼0.22 ppb, hitherto unprecedented. The observed selectivity to CH4 over non-polar CO2, polar volatile organic compounds, and moisture has roots in competing electron-sharing mechanisms at its different adsorption sites. This important result provides a significant reference to guide future MOF-related composite research to achieve the best sensing performance. On molecular adsorption, MWCNTs facilitate electrical transport via manipulating the ZIF-8 band gap to show a p-type semiconductor behavior with lower activation energy to induce a measurable resistance change. Excellent repeatability and reversibility are shown. A carbon-engineered MOF composite has the potential to actuate similar selective response to low reactive gases via carrier manipulation in the energy band gap.
Mid-infrared (IR) photothermal spectroscopy of adsorbed molecules is an ideal technique for molecular recognition in miniature sensors with very small thermal mass. Here, we report on combining the ...photothermal spectroscopy with electrical resonance of a semiconductor nanowire for enhanced sensitivity, selectivity, and simplified readout. Wide band gap semiconductor bismuth ferrite nanowire, by virtue of its very low thermal mass and abundance of surface states in the band gap, facilitates thermally induced charge carrier trapping in the surface states, which affects its electrical resonance response. Electrical resonance response of the nanowire varies significantly depending on the photothermal spectrum of the adsorbed molecules. We demonstrate highly selective detection of mid-IR photothermal spectral signatures of femtogram level molecules physisorbed on a nanowire by monitoring internal dissipation response at its electrical resonance.
Current robotic systems have achieved great sophistication in kinematic motion, control, and neural processing. One of the most challenging limitations imposed on modern robotics is the portable ...power source needed to sustain tether-free operation. Energy storage devices such as batteries and combustion engines may be heavy, require a great deal of space, and invariably have a finite energy capacity. Methods to control such devices may also impose limitations as most robotic systems rely on either tethered or radiative communication. The unavoidable repercussion of these limitations is the ultimate reduction of mobility and operation time to achieve specific tasks. To address these challenges, we apply our quasi-wireless powering methodology to show the operation of two robotic devices over a 1×1 m
2
surface. Both power and control signals are transmitted simultaneously, producing seamless storage-free functionality over the entire area with a communication technique that is not line-of-sight or radiation dependent. We demonstrate an average power transfer efficiency of 93% using commercially available toy robots and discuss parameters relating to the power and communication performance.
Standoff detection based on optical spectroscopy is an attractive method for identifying materials at a distance with very high molecular selectivity. Standoff spectroscopy can be exploited in ...demanding practical applications such as sorting plastics for recycling. Here, we demonstrate selective and sensitive standoff detection of polymer films using bi-material cantilever-based photothermal spectroscopy. We demonstrate that the selectivity of the technique is sufficient to discriminate various polymers. We also demonstrate in situ, point detection of thin layers of polymers deposited on bi-material cantilevers using photothermal spectroscopy. Comparison of the standoff spectra with those obtained by point detection, FTIR, and FTIR-ATR show relative broadening of peaks. Exposure of polymers to UV radiation (365 nm) reveal that the spectral peaks do not change with exposure time, but results in peak broadening with an overall increase in the background cantilever response. The sensitivity of the technique can be further improved by optimizing the thermal sensitivity of the bi-material cantilever and by increasing the number of photons impinging on the cantilever.
2D metal–organic frameworks (MOFs) offer high surface area and unique accessibility to active adsorption sites making them appealing for gas sensing applications. 2D MOFs‐based sensors are gaining ...traction for detecting hazardous flu‐gases such as ammonia selectively at low concentrations. Fluorescent and colorimetric sensing are promising techniques offering high sensitivity, selectivity, and rapid response in simple applications. In this work, Zn‐BTC is synthesized as 2D‐MOFs nanosheet with approximate thickness of 2.52 nm via a fast, facile, direct synthesis technique. The introduction of 8‐hydroxyquinoline during synthesis forms fluorescent compounds with zinc (ZnQ) which is encapsulated and decorated onto Zn‐BTC. Inherent charges on ZnQ lead to the agglomeration of multiple 2D‐flakes forming ZnQ@Zn‐BTC multi‐flaked nano‐discs. The synthesized material shows visible color change upon exposure to ammonia from white to ivory. In addition, selective fluorescence quenching is observed under ultraviolet illumination (λex = 365 nm) when ZnQ@Zn‐BTC is exposed to ammonia. The limit of detection reaches 0.27 ppm as a dried film for gaseous sensing and 60.8 nm in liquid phase fluorescence quenching, respectively. The observed high sensitivity and selectivity are attributed to the manipulation of active sites of 2D‐MOFs nanosheet with ZnQ. Functionalization also limits the degradation and breakdown of ZnQ@Zn‐BTC.
Enhanced colorimetric and fluorescent ammonia sensing with ZnQ@Zn‐BTC nano‐discs.
PDF
