The development of materials toward ppb-level nitric oxide (NO) sensing at room temperature remains in high demand for the monitoring of respiratory inflammatory diseases. In order to find an iron-containing molecule without steric hindrance to combine with graphene for room temperature NO gas sensing, here a supramolecular assembly of ferrocene (Fc) and reduced graphene oxide (rGO) was designed and prepared for NO sensing. The assembly of Fc/rGO was characterized using FT-IR, TEM, and XPS measurements. The Fc/rGO-based sensors exhibited superior NO sensing properties at room temperature including high response (R_a/R_g = 1.73, 1 ppm), high selectivity against other exhaled gases, reliable repeatability and stability (less than 4 % decrease after 40 days). A practical limit of detection (LOD) of 200 ppb was achieved. The theoretical simulation demonstrates that ferrocene is assembled via π-π interaction with rGO in edge-to-face configuration which provides relatively lower energy than face-to-face configuration does for the whole assembly. It was first verified that the enhanced adsorption capacity and the charge transfer between NO and Fc/rGO would result in improvement of the assembly's sensitivity toward NO after ferrocene was assembled with graphene. This work provides a fresh approach of anchoring iron on graphene for gas sensing via supramolecular methods.

The significant in situ multicolored patterning without changing printing tools nor substrate media still remains challenging, especially toward practical applications for anti-counterfeiting. This research invented a unique universal approach for the laser-induced in situ synthesis of colorful fluorescent patterns (from blue: CIE 0.15, 0.18 to red orange: CIE 0.36, 0.39) through the controlled formation of N, S doped carbon dots (CDs) in solid composite polymer films or hydrogel with a hierarchical and physically unclonable microsurface architecture for anti-counterfeiting. The in situ patterning approach, coupled with multi-layer technique, yielding designable blue, yellow, orange, and red orange color under 365 nm in the same pattern. A 5 cm² colorful pattern can be efficiently finished within 5 min without changing the substrate and the line width accuracy can be up to 300 μm. The absolute quantum efficiency of the blue pattern reached as high as 23%. The fluorescent patterns can be survived at indoor for 24 months. The hydrogen bonding interactions between the CDs precursor and polymer facilitated the generation, uniform dispersion and stabilization of CDs during the laser irradiation. The hypothesis that laser irradiation induced photochemical reactions of CD precursors within a polymer matrix was supported by thermodynamic assessments. The universality of in situ fluorescent patterning strategy was demonstrated by developing fluorescent patterns on both solid polymer films, hydrogel, pharmaceutical packaging and textile.

Fractional exhaled nitric oxide (FeNO) can be used to describe inflammatory processes in the respiratory tract. Directly detecting ppb-level nitric oxide (NO) with chemiresistive sensors at room temperature faces the challenges of simultaneously obtaining high sensitivity and high stability for sensors. We aimed to improve the stability and sensitivity of NO sensors. We assembled sheet-like porphyrin-based MOF DLS-2D-Co-TCPP(Fe) with 5-aminonaphthalene-1-sulfonic acid-rGO (ANS-rGO) nanosheets through coordination interactions. In this way, we offered a room-temperature NO-sensing hybrid, DLS-2D-Co-TCPP(Fe)/ANS-rGO, with a sheet-on-sheet (SOS) architectural heterojunction. The DLS-2D-Co-TCPP(Fe)/ANS-rGO-based sensor demonstrated superior NO-sensing performance, including high sensitivity (R_a/R_g = 1.33, 250 ppb), reliable repeatability, high selectivity, and fast response/recovery (150 s/185 s, 1 ppm) at a sensing concentration from 100 ppb to 10 ppm at room temperature. The obtained sensor showed high stability, retaining >85% of its initial response after 60 days. Designing NO-responsive Fe-N₄ active units containing MOF nanosheets, along with constructing a heterojunction with an SOS architecture to facilitate carrier migration, collaboratively dominated the superior performance of synthesized NO sensors. This work provides a strategy for designing SOS architectural heterojunctions to obtain high-performance MOF-based gas-sensing materials.

Inspired by the CO₂-induced reversible activation mechanism of the slow anion channel 1 (SLAC1) in plant stomatal guard cells during plant photosynthesis, we designed and prepared a CO₂- switchable H⁺/OH⁻ ion channel (CSPH ion channel). A high-performance chemiresistive room temperature CO₂ sensor has been prepared based on this CSPH ion channel. The obtained CO₂ room temperature sensor γ-CD-MOF@RhB exhibits high sensitivity (R_g/R₀ = 1.50, 100 ppm), excellent selectivity, good stability (less than 5% reduction in 30 days response value), and 99.96% consistency with commercial infrared CO₂ meter. The practical limit of detection (pLOD) of the γ-CD-MOF@RhB sensor reaches 10 ppm at room temperature toward CO₂, which is the lowest for reported MOF-derived chemiresistive room temperature CO₂ sensors so far. Ion conduction mechanism studies have shown that the CSPH ion channel behaves as a CO₂-switchable H⁺/OH⁻ ion channel with a switching point of approximately 60 000 ppm CO₂. As an application attempt, the fabricated low pLOD CO₂ sensor has been used for human exhaled CO₂ detection to compare CO₂ concentration in the breath of individuals before and after exercise and COVID-19. It was also logically indicated that the average concentration of human exhaled CO₂ after COVID-19 recovery is different for undiseased subjects.

It is a great challenge to develop efficient room-temperature sensing materials and sensors for nitric oxide (NO) gas, which is a biomarker molecule used in the monitoring of inflammatory respiratory diseases. Herein, Hemin (Fe (III)-protoporphyrin IX) is introduced into the nitrogen-doped reduced graphene oxide (N-rGO) to obtain a novel sensing material HNG-ethanol. Detailed XPS spectra and DFT calculations confirm the formation of carbon–iron bonds in HNG-ethanol during synthesis process, which act as electron transport channels from graphene to Hemin. Owing to this unique chemical structure, HNG-ethanol exhibits superior gas sensing properties toward NO gas (R_a/R_g = 3.05, 20 ppm) with a practical limit of detection (LOD) of 500 ppb and reliable repeatability (over 5 cycles). The HNG-ethanol sensor also possesses high selectivity against other exhaled gases, high humidity resistance, and stability (less than 3% decrease over 30 days). In addition, a deep understanding of the gas sensing mechanisms is proposed for the first time in this work, which is instructive to the community for fabricating sensing materials based on graphene-iron derivatives in the future.

Fluorescent patterns with multiple functions enable high-security anti-counterfeiting labels. Complex material synthesis and patterning processes limit the application of multifunctional fluorescent patterns, so the technology of in situ fluorescent patterning with tunable multimodal capabilities is becoming more necessary. In this work, an in situ fluorescent patterning technology was developed using laser direct writing on solid cellulose film at ambient conditions without masks. The fluorescent intensity and surface microstructure of the patterns could be adjusted by programmable varying of the laser parameters simultaneously. During laser direct writing, carbon dots are generated in situ in a cellulose ester polymer matrix, which significantly simplifies the fluorescent patterning process and reduces the manufacturing cost. Interestingly, the tunable fluorescent intensity empowers the fabrication of visual stereoscopic fluorescent patterns with excitation dependence, further improving its anti-counterfeiting performance. The obtained fluorescent patterns still show ultrahigh optical properties after being immersed in an acid/base solution (pH 5-12) over one month. In addition, the anti-UV performance of the obtained laser-patterned film with transmittance around 90% is comparable to that of commercial UV-resistant films. This work provided an advanced and feasible approach to fabricating programmable, performance-tunable, subtle fluorescent patterns in large-scale for industrial application.

Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N4 active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (Ra/Rg = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N4 active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.