“Enzyme‐Like” Spatially Fixed Polyhydroxyl Microenvironment‐Activated Hydrochromic Molecular Switching for Naked Eye Detection of ppm Level Humidity

Abstract

To avoid affecting the highly efficient photoelectric conversion of the solar cells, the moisture content of the production workshop should be less than 1 ppm. The preparation of lithium-ion batteries, organic light-emitting devices, optical fibers, and supercapacitors requires humidity conditions of <0.1 ppm. In addition, power transmission (which requires insulating/ anhydrous gas), aviation exploration, and scientific research involve monitoring/ identifying the trace levels of moisture. [3,4] Therefore, the development of technologies or products that can accurately detect and indicate ultralow (<100 ppm) or extremely low (<1 ppm) humidity is of great practical significance.Currently, only semiconductor capacitive sensors based on special crystal forms (i.e., γ-Al 2 O 3 ) and mirror-based dew point hygrometers can achieve accurate detection of ultralow or trace amounts of moisture, with thresholds of 1 ppm and −100 °C of dew point (i.e., 0.01 ppm), respectively. [5,6] However, owing to the complex and harsh manufacturing of core materials and the extremely high requirements for instrument components (such as high-quality mirror surfaces, high-precision temperature control systems and high-sensitivity dewdrop and ice crystal optical detection systems), these instruments are bulky, extremely expensive and require complex external power supply systems or coupling circuits, significantly limiting their widespread application. As an alternative, color-visualized waterresponsive materials offer a simple, low-cost, portable and easy-to-read method for humidity sensing and detection. They provide a direct visual way to convert environmental water vapor stimuli into a naked eye readout color by incorporating humidity-responsive chromic components into a solid support, and the resulting visual humidity sensor can be adapted to different environmental conditions. Thus far, various novel systems/strategies have been developed for visual humidity sensors, including inorganic materials (e.g., cobalt/nickel halides, [7,8] perovskites, [9] and nanocrystals [10] ), photonic bandgap structure materials, [11][12][13][14][15] aggregation discoloration dyes, [16][17][18][19] metal dynamic coordination systems, [20] polaritysensitive fluorescent materials, [21] redox [22] and acid-base [23] color-changing dye switches. These efforts have significantlyThe detection and monitoring of ultralow humidity (<100 ppm) are critical in many important industries, such as high-tech manufacturing, scientific research, and aerospace. However, the development of ppm level humidity sensors with portability, low cost, and ease of regeneration remains a significant challenge. Herein, an innovative "enzyme-like" construction strategy is proposed to address this problem by employing suitable molecular-level humidity-sensitive units and chemically constructing a multilevel spatial synergistic sensitization microenvironment around it. The as-prepared ultralow humidity-sensitive paper (UHSP) achieved a naked eye recognition humidity of 0.01-100 ppm....

A PN(Pz)P ligand protected Au2Cu2complex for photoluminescent ultra-low humidity detection with reversible single-crystal-to-single-crystal transformations

“…These emissions were red-shifted by 12 nm (CaCl 2 and KOH) and 8 nm (P 2 O 5 ) compared to that of anhydrous 1 (in a vacuum), indicating that 1 was capable of detecting ultra-low humidity changes even in P 2 O 5 dried air. This detection limit is comparable to the lowest recorded value of 0.01-100 ppm, determined using nitro-oxazolidine as the sensory material, 4 and is lower than those of other reported optical sensory materials, 51,52 including 1 ppm for SrF 2 :Eu 3+ @TTA nanoparticles 53 and 248 ppm (w/w) for perovskite CH 3 NH 3 PbBr 3 . 54 The reversibility between 1 and 1•2H 2 O was further verified by alternatively placing 1•2H 2 O in a vacuum and air, over 5 cycles (Fig.…”

“…Reliable and sensitive detection of ultra-low humidity is critical for many processes, during which the moisture content needs to be strictly monitored and/or controlled, for example under 500 ppm in microelectronic packaging, 1 55 ppm in the aviation industry, 2 10 ppm during reactions involving Grignard and organolithium reagents, 3 and 0.1 ppm in lithium-ion battery manufacturing. 4 Current technology shows good sensitivity in the detection of ultra-low humidity. The most common capacitive sensors consisting of aluminum oxide (γ-Al 2 O 3 ) nanoporous films have achieved a humidity detection range of 3.7-100 ppm.…”

“…5 “Enzyme-like” humidity-sensitive chromic materials have achieved naked-eye humidity detection from 0.01–100 ppm. 4 These methods required external electronic circuits or suffered from irreversibility. It is highly desirable to develop more reversible low humidity sensing materials for these important applications.…”

Recent research progress of selenotungstate-based biomolecular sensing materials

“…The precision in their sensing selectivity and activity can be controlled through modifying the sizes and coordination microenvironments of these nanomaterials. [54][55][56][57] According to the detection mechanism of sensing materials, electrochemical biosensors are generally classified into two categories: electrochemical catalytic biosensors (ECBs) and EABs. 58…”