Advancing Intelligent Organ-on-a-Chip Systems with Comprehensive In Situ Bioanalysis

In vitro models are essential to a broad range of biomedical research, such as pathological studies, drug development, and personalized medicine. As a potentially transformative paradigm for 3D in vitro models, organ-on-a-chip (OOC) technology has been extensively developed to recapitulate sophisticated architectures and dynamic microenvironments of human organs by applying the principles of life sciences and leveraging micro- and nanoscale engineering capabilities. A pivotal function of OOC devices is to support multifaceted and timely characterization of cultured cells and their microenvironments. However, in-depth analysis of OOC models typically requires biomedical assay procedures that are labor-intensive and interruptive. Herein, the latest advances toward intelligent OOC (iOOC) systems, where sensors integrated with OOC devices continuously report cellular and microenvironmental information for comprehensive in situ bioanalysis, are examined. It is proposed that the multimodal data in iOOC systems can support closed-loop control of the in vitro models and offer holistic biomedical insights for diverse applications. Essential techniques for establishing iOOC systems are surveyed, encompassing in situ sensing, data processing, and dynamic modulation. Eventually, the future development of iOOC systems featuring cross-disciplinary strategies is discussed.

In Situ Tyrosinase Monitoring by Wearable Microneedle Patch toward Clinical Melanoma Screening

Despite the potential indicating role of tyrosinase (TYR) in cutaneous melanoma, how to capture the real changes of TYR in suspicious skin remains a major challenge. Unlike the traditional human serum test, this study reports a sensing platform that incorporates a wearable microneedle (MN) patch and trimetallic Au@Ag-Pt nanoparticles (NPs) for surface-enhanced Raman scattering (SERS) and colorimetric dual-mode detecting TYR in human skin in situ toward potential melanoma screening. In the presence of TYR, catechol immobilized on MN is preferentially oxidized to benzoquinone, which competitively impedes the interaction of MN and Au@Ag-Pt NPs, triggering the SERS-colorimetric signal reciprocal switch. Using a B16F10 mouse melanoma model, our platform is capable of noninvasively piercing the skin surface and detecting TYR levels before and during anti-PD-1 antibody treatment, which would be highly informative for prognostic judgment and illness monitoring of melanoma. Through in situ sensing for capturing the metabolic changes of TYR in advance, this platform was successfully applied to discriminate the melanoma subjects from skin moles and normal ones (p < 0.001), as well as screen potential melanoma from lactate dehydrogenase (LDH)-negative patients. Melanoma growth and prognosis can still be monitored through recording the continuous change of TYR levels. More importantly, the well-defined flexible and stretchable characteristics of the MN patch allow robustly adhering to the skin without inducing chemical or physical irritation. We believe this platform integrating MN-based in situ sensing, TYR responsiveness, and SERS/colorimetric dual-readout strategy will have high clinical importance in early diagnosis and monitoring of cutaneous melanoma.

Laser Velocimetry for the In Situ Sensing of Deep-Sea Hydrothermal Flow Velocity

Laser Doppler velocimetry (LDV) based on a differential laser Doppler system has been widely used in fluid mechanics to measure particle velocity. However, the two outgoing lights must intersect strictly at the measurement position. In cross-interface applications, due to interface effects, two beams of light become easily disjointed. To address the issue, we present a laser velocimeter in a coaxial arrangement consisting of the following components: a single-frequency laser (wavelength λ = 532 nm) and a Twyman-Green interferometer. In contrast to previous LDV systems, a laser velocimeter based on the Twyman-Green interferometer has the advantage of realizing cross-interface measurement. At the same time, the sensitive direction of the instrument can be changed according to the direction of the measured speed. We have developed a 4000 m level laser hydrothermal flow velocity measurement prototype suitable for deep-sea in situ measurement. The system underwent a withstand voltage test at the Qingdao Deep Sea Base, and the signal obtained was normal under a high pressure of 40 MPa. The velocity contrast measurement was carried out at the China Institute of Water Resources and Hydropower Research. The maximum relative error of the measurement was 8.82% when compared with the acoustic Doppler velocimeter at the low-speed range of 0.1-1 m/s. The maximum relative error of the measurement was 1.98% when compared with the nozzle standard velocity system at the high-speed range of 1-7 m/s. Finally, the prototype system was successfully evaluated in the shallow sea in Lingshui, Hainan, with it demonstrating great potential for the in situ measurement of fluid velocity at marine hydrothermal vents.

A Conductive Hydrogel Microneedle-Based Assay Integrating PEDOT:PSS and Ag-Pt Nanoparticles for Real-Time, Enzyme-Less, and Electrochemical Sensing of Glucose

Continuous glucose meters (CGMs) have tremendously boosted diabetes care by emancipating millions of diabetic patients' need for repeated self-testing by pricking their fingers every few hours. However, CGMs still suffer from major deficiencies regarding accuracy, precision, and stability. This is mainly due to their dependency on an enzymatic detection mechanism. Here a low-cost hydrogel microneedle (HMN)-CGM assay fabricated using swellable dopamine (DA)-hyaluronic acid (HA) hydrogel for glucose interrogation in dermal interstitial fluid (ISF) is introduced. Platinum and silver nanoparticles are synthesized within the 3D porous hydrogel scaffolds for nonenzymatic electrochemical sensing of the glucose. Incorporation of a highly water dispersible conductive polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) enhances the electrical properties of HMN array, making the patch suitable as the working electrode of the sensor. The in vitro and ex vivo characterization of this newly developed HMN patch is fully studied. The performance of the HMN-CGM for real-time measurement of glucose is also shown using a rat model of type 1 diabetes. The device introduces the first HMN-based assay for tracking important disease biomarkers and expect to pave the way for next generation of polymeric-based sensors.

Temperature Self-Calibration of Always-On, Field-Deployed Ion-Selective Electrodes Based on Differential Voltage Measurement

Originally developed for use in controlled laboratory settings, potentiometric ion-selective electrode (ISE) sensors have recently been deployed for continuous, in situ measurement of analyte concentration in agricultural (e.g., nitrate), environmental (e.g., ocean acidification), industrial (e.g., wastewater), and health-care sectors (e.g., sweat sensors). However, due to uncontrolled temperature and lack of frequent calibration in these field applications, it has been difficult to achieve accuracy comparable to the laboratory setting. In this paper, we propose a novel temperature self-calibration method where the ISE sensors can serve as their own thermometer and therefore precisely measure the analyte concentration in the field condition by compensating for the temperature variations. We validate the method with controlled experiments using pH and nitrate ISEs, which use the Nernst principle for electrochemical sensing. We show that, using temperature self-calibration, pH and nitrate can be measured within 0.3% and 5% of the true concentration, respectively, under varying concentrations and temperature conditions. Moreover, we perform a field study to continuously monitor the nitrate concentration of an agricultural field over a period of 6 days. Our temperature self-calibration approach determines the nitrate concentration within 4% of the ground truth measured by laboratory-based high-precision nitrate sensors. Our approach is general and would allow battery-free temperature-corrected analyte measurement for all Nernst principle-based sensors being deployed as wearable or implantable sensors.

In Situ Monitoring of Powder Bed Fusion Homogeneity in Electron Beam Melting

Increasing attention has been devoted in recent years to in situ sensing and monitoring of the electron beam melting process, ranging from seminal methods based on infrared imaging to novel methods based on backscattered electron detection. However, the range of available in situ monitoring capabilities and solutions is still quite limited compared to the wide number of studies and industrial toolkits in laser-based additive manufacturing processes. Some methods that are already industrially available in laser powder bed fusion systems, such as in situ detection of recoating errors, have not yet been investigated and tested in electron beam melting. Motivated by the attempt to fill this gap, we present a novel in situ monitoring methodology that can be easily implemented in industrial electron beam melting machines. The method is aimed at identifying local inhomogeneity and irregularities in the powder bed by means of layerwise image acquisition and processing, with no external illumination source apart from the light emitted by the hot material underneath the currently recoated layer. The results show that the proposed approach is suitable to detect powder bed anomalies, while also highlighting the link between the severity of in situ detected errors and the severity of resulting defects in the additively manufactured part.

Preventing Memory Effects in Surface-Enhanced Raman Scattering Substrates by Polymer Coating and Laser-Activated Deprotection

The development of continuous monitoring systems requires in situ sensors that are capable of screening multiple chemical species and providing real-time information. Such in situ measurements, in which the sample is analyzed at the point of interest, are hindered by underlying problems derived from the recording of successive measurements within complex environments. In this context, surface-enhanced Raman scattering (SERS) spectroscopy appears as a noninvasive technology with the ability of identifying low concentrations of chemical species as well as resolving dynamic processes under different conditions. To this aim, the technique requires the use of a plasmonic substrate, typically made of nanostructured metals such as gold or silver, to enhance the Raman signal of adsorbed molecules (the analyte). However, a common source of uncertainty in real-time SERS measurements originates from the irreversible adsorption of (analyte) molecules onto the plasmonic substrate, which may interfere in subsequent measurements. This so-called "SERS memory effect" leads to measurements that do not accurately reflect varying conditions of the sample over time. We introduce herein the design of plasmonic substrates involving a nonpermeable poly(lactic-co-glycolic acid) (PLGA) thin layer on top of the plasmonic nanostructure, toward controlling the adsorption of molecules at different times. The polymeric layer can be locally degraded by irradiation with the same laser used for SERS measurements (albeit at a higher fluence), thereby creating a micrometer-sized window on the plasmonic substrate available to molecules present in solution at a selected measurement time. Using SERS substrates coated with such thermolabile polymer layers, we demonstrate the possibility of performing over 10,000 consecutive measurements per substrate as well as accurate continuous monitoring of analytes in microfluidic channels and biological systems.

A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide

Trace gas concentration measurements in the stratosphere and troposphere are critically required as inputs to constrain climate models. For this purpose, measurement campaigns on stratospheric aircraft and balloons are being carried out all over the world, each one involving sensors which are tailored for the specific gas and environmental conditions. This paper describes an automated, portable, mid-infrared quantum cascade laser spectrometer, for in situ carbon monoxide mixing ratio measurements in the stratosphere and troposphere. The instrument was designed to be versatile, suitable for easy installation on different platforms and capable of operating completely unattended, without the presence of an operator, not only during one flight but for the whole period of a campaign. The spectrometer features a small size (80 × 25 × 41 cm3), light weight (23 kg) and low power consumption (85 W typical), without being pressurized and without the need of calibration on the ground or during in-flight operation. The device was tested in the laboratory and in-field during a research campaign carried out in Nepal in summer 2017, onboard the stratospheric aircraft M55 Geophysica. The instrument worked extremely well, without external maintenance during all flights, proving an in-flight sensitivity of 1–2 ppbV with a time resolution of 1 s.

Preparation of a Smart and Portable Film for in Situ Sensing of Iron Microcorrosion

Corrosion of iron-containing materials, which presents serious economic and safety problems, normally begins with microcorrosion, which refers to the early stages of corrosion before visible changes appear on the surface. If microcorrosion could be detected and repaired immediately, corrosion damage could be greatly reduced. Current technology and materials, however, are not able to detect microcorrosion of iron in a cheap and convenient manner. Here, we have used a natural product, ellagic acid (EA), to fabricate an EA-functionalized poly(vinyl alcohol) (PVA) film (EAF) for in situ sensing of the initial stage of microcorrosion. EAF was able to effectively sense iron microcorrosion via an obvious color change. The film also had good long-term stability and mechanical strength. Since EAF can be easily prepared from inexpensive and green raw materials, the film opens up a new opportunity for the detection of iron microcorrosion.