4D-printed pH sensing claw

Recent Advances in 4D Printing of Advanced Materials and Structures for Functional Applications

4D printing has attracted tremendous worldwide attention during the past decade. This technology enables the shape, property, or functionality of printed structures to change with time in response to diverse external stimuli, making the original static structures alive. The revolutionary 4D-printing technology offers remarkable benefits in controlling geometric and functional reconfiguration, thereby showcasing immense potential across diverse fields, including biomedical engineering, electronics, robotics, and photonics. Here, a comprehensive review of the latest achievements in 4D printing using various types of materials and different additive manufacturing techniques is presented. The state-of-the-art strategies implemented in harnessing various 4D-printed structures are highlighted, which involve materials design, stimuli, functionalities, and applications. The machine learning approach explored for 4D printing is also discussed. Finally, the perspectives on the current challenges and future trends toward further development in 4D printing are summarized.

Colorimetric and fluorescence dual-mode pH sensor based on nitrogen-doped carbon dots and its diverse applications

A dual-mode pH sensor based on nitrogen-doped carbon dots (N-CDs) with the source of o-phenylenediamine and tryptophan has been constructed. Under the stimulation of pH, the N-CDs exhibited prominent both color and fluorescence changes, leading to the rarely discovered colorimetric and fluorescent dual-readouts for the evaluation of pH. The mathematic relationship was established between pH and fluorescence intensity of N-CDs, and between pH and the UV-Vis absorbance ratio at 630 nm and 488 nm of N-CDs, respectively, over a quite broad pH range of 2.2 to 12.0. Multiple techniques are used to explore the dual-mode pH-responsive mechanism, and the preliminary explanation is put forward. The experimental results show that the N-CDs have visualized pH sensing applicability for actual samples, including various water samples and HeLa cell. Furthermore, the N-CD ink is developed for successful information encryption and anti-counterfeiting. This work might provide valuable insights into the sensing mechanism of CDs, and the application potential of CDs in broader fields.

A 3D-printed millifluidic device for triboelectricity-driven pH sensing based on ZnO nanosheets with super-Nernstian response

This paper suggests a straightforward and rapid fabrication method applying the integration of 3D printing and triboelectric nanogenerator (TENG) technologies to realize milli/microfluidic multipurpose devices. The proposed liquid-solid TENG device is served as an energy harvester and sensor at the same time with flexibility in operation modes. Accordingly, an innovative ethylene vinyl acetate (EVA)-made millifluidic pH sensor is fabricated based on zinc oxide nanosheets as a showcase of the functional adaptability of the ubiquitous device, and its performance is analyzed and compared with contemporary electrochemical pH sensors. High crystallinity of the nanosheets with an incline to (103) orientation in parallel with high levels of oxygen vacancies provides capacity for surface charge accumulation at the nanosheet-aqueous solution interface and the ensuing ultrahigh sensitivity of the triboelectric sensor. The millichannel is optimized in terms of sensing surface area, flow rate, and hydrophobicity properties by opting for appropriate geometry, TENG operation modes, and materials. Despite the finding that quasi-single-electrode mode TENG experiences a higher response (8.12 × Nernst limit) in comparison with quasi-contact-separation configuration (4.14 × Nernst limit), the latter enjoys superior linearity, stability, repeatability, reproducibility, and reliability characteristics corresponding to R² of 98.93%, drift rate of 13 mV/h, relative standard deviation (RSD) of 1.23% in third hysteresis loop, 2.24%, and maximum standard error of ±0.2 pH units across multiple trials, respectively, in a wide pH range of 2-13. Time- and cost-effectiveness, user-friendliness, self-powering, portability, and biocompatibility of the device could be asserted as considerable advantages to open the door for feasibly realizing the new generation of real-life and point-of-care devices.