Dual-mode Sensor Research Articles

High-sensitivity luminescent thermometer based on Mn4+/Sm3+ dual-emission centers in double-perovskite tellurate

Precise temperature detection utilizing optical parameters is very important and has accelerated scientific researchers to design more suitable materials for non-contact optical thermometers. However, the obstacles of low sensitivity, narrow temperature range, and poor signal discrimination are the main challenges at present. Herein, a dual-mode optical thermometer via the fluorescence intensity ratio (FIR) and decay lifetime was designed in novel double-perovskite Mn4+/Sm3+ co-doped SrGdLiTeO6 (SGLT: Mn4+, Sm3+) luminescent materials. The crystal structure, elemental mapping, elemental valence, and oxygen vacancy were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and electron paramagnetic resonance, respectively. Under 464 nm excitation, the maximum relative sensitivity (SR) values based on the FIR and decay lifetime techniques were estimated as 8.69% K−1@573 K and 1.3% K−1@520 K, respectively. Markedly, the SGLT:1.2%Mn4+, 1.5%Sm3+ phosphor exhibited a good signal discriminability. This work identified a new type of luminescent material to explore rigorous and valid dual-mode optical temperature sensors with a wide range and high sensitivity.

A Textile Proximity/Pressure Dual-Mode Sensor Based on Magneto-Straining and Piezoresistive Effects

The demand for flexible tactile sensors with both contact and contactless sensing capabilities is growing rapidly in the fields of smart robotics and prosthesis. However, it is still a challenge to integrate high performance proximity and pressure sensing functions in one sensor through simple fabrication process. Here, we propose a textile-based dual-mode sensor that can work on both magneto-straining mode (proximity) and piezoresistive mode (pressure). The sensor is simply fabricated by coating two functional materials in a concentric pattern, i.e., a magnetic layer followed by a conductive layer made of 2D MXene composite, on spandex substrate. As the dual-mode sensor approaches to a magnetic object, the attractive magnetic force will stretch the magnetic layer, along with the conductive layer. The strained conductive layer causes an increase of the resistance. Upon contact, the magnetic force reaches its maximum, while the pressure force works against the magnetic force and starts to reduce the strain of the conductive layer, leading to a decrease of the resistance. The turning point of the resistance can be used to identify the contact moment, and as an indicator of the switching of the two working modes of the sensor. Benefitting from the superior conductivity of the MXene material in the conductive layer, high sensitivity for both proximity sensing (13.76 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) and pressure sensing (0.7 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) was achieved. The proposed dual-mode sensing methodology has great potential in human-machine interaction (HMI) applications.

Dual-Mode Flexible Capacitive Sensor for Proximity-Tactile Interface and Wireless Perception

Flexible sensors with proximity and tactile sensing have attracted great interest in electronic skins (E-skin), human-machine interfaces (HMI), and soft robotics. However, it remains challenging to have both proximity and haptic sensing ability in one flexible device, yet enable wireless sensing. Here, based on the edge electric field and piezo-capacitive effect, we successfully present a combination of approaching non-contact sensation with pressure perception in one flexible dual-mode capacitive sensor (FDCS) which possesses both proximity-tactile interface interaction and wireless sensing. Large scale and low-cost methods of the screen printing and the laser engraving are selectively used to fabricate flexible electrodes and cone-pattern mold, respectively. Thanks to the stable conductivity of the electrodes and the micro-cone-like dielectric structure, the FDCS exhibits a detection distance of up to 20 cm in proximity mode and an extended operating range of 200 kPa, a low detection limit (10.2 Pa), fast response time (90 ms), and long endurance (>10,000 cycles) in pressure mode. A 64-unit pressure matrix successfully interacted with the coupling of the proximity finger and the actual pressure in two different modes. In addition, by assembling the FDCS with a planar spiral coil to form an LC (inductance-capacitance) resonator, rather than connecting directly to an LCR device, the device was able to detect external pressure wirelessly. The development of this dual-mode sensor and its demonstration paves the way for potential flexible sensors for applications in HMI and soft robots.

Artificial neural networks assisting the design of a dual-mode photonic crystal nanobeam cavity for simultaneous sensing of the refractive index and temperature.

We put forward a dual-mode photonic crystal nanobeam cavity for simultaneous sensing of the refractive index (RI) and temperature (T) designed with the assistance of artificial neural networks (ANNs). We choose the structure of quadratically tapered elliptical holes with a slot to improve the sensitivities of the two modes. To reduce the time consumption of the design, the ANNs are trained to predict the band structure and to inverse design the geometric structure. For the forward prediction and the inverse design neural networks, low mean square errors of 5.1×10-4 and 1.4×10-2 are achieved, respectively. Through a specific design of band properties by the well-trained neural networks, a dual-mode nanobeam sensor with high quality factors of 9.34×104 and 1.55×105 and a small footprint of 23.8×0.7µm2 are designed. The RI and T sensitivities of the air mode are 405 nm/RIU and 40 pm/K, respectively, whereas those of the dielectric mode are 531 nm/RIU and 27 pm/K, respectively. The present work shows significance in further research on the design and applications for dual-mode cavities.

Porous graphene foam composite-based dual-mode sensors for underwater temperature and subtle motion detection

Soft multimodal sensors in practical applications for health monitoring and human–machine interfaces require them to show sufficiently high sensitivity over wide sensing rages, rapid response and excellent durability, and waterproof property. Herein, we demonstrate a dual-mode sensor based on a porous graphene foam composite to achieve the aforementioned challenging yet attractive performance parameters for strain and temperature sensing. The resulting dual-mode sensor exhibits a strain sensitivity of 2212.5 in the wide piecewise linear range of 0–65%, a rapid response of 0.11 s, an ultralow detection limit of 0.0167%, and outstanding stability over 15,000 cycles. The sensor can also detect temperature with a high sensitivity of 0.97 × 10-2 °C -1 over a wide linear range of 10–185 °C and a small detection limit for sensing both low- and high-temperature environments. Taken together with the waterproof property, the dual-mode sensor can accurately monitor the large, small, and even subtle motions and temperature variations in both dry and underwater conditions. The capability to detect the subtle yet rapidly changing motions from distal arteries and skeletal muscles paves the way for the development of future soft multimodal, waterproof electronic sensing devices toward human–computer interaction, health monitoring and early disease prevention, and personalized medicine.

A dual-mode self-referenced optical thermometry with high sensitivity based on Er3+-Yb3+ co-doped Sr2YTaO6 thermochromic phosphor

Up conversion luminescent materials Sr2YTaO6: Er3+, Yb3+ phosphors were prepared by high temperature calcination. In view of the formation, temperature characteristics, and photoluminescence features of the sample, X-ray diffraction and photoluminescence were used. Under the excitation at 980 nm, the series of samples is significantly stimulated by Er3+ up-conversion luminescence and Yb3+ sensitization at 524, 550 and 659 nm. According to the diversity of temperature sensing performance from these three highest peaks, a dual-mode temperature sensor on account of fluorescence intensity ratio (thermally coupled level between 2H11/2 and 4S3/2, and nonthermally coupled energy levels between 2H11/2 and 4F9/2) is achieved by using a single luminescent center. Moreover, the phosphor has strong thermal stability, which is helpful to improve the accuracy of temperature measurement. Under the temperature measurement of a dual-mode temperature sensor, it is calculated that the optimal absolute sensitivity Sa of thermally coupled energy level is 0.78 × 10−3 K−1 (473 K) and relative sensitivity Sr is 1.32 %K−1 (293 K), and the maximum optimal absolute sensitivity Sa of non-thermally coupled energy level is 1.02 × 10−4 K−1 (473 K) and relative sensitivity Sr is 0.58 %K−1 (293 K). All results imply that Sr2YTaO6: Er3+, Yb3+ phosphors are promising materials for self-referenced optical temperature measurement.

A flexible dual-mode pressure sensor with ultra-high sensitivity based on BTO@MWCNTs core-shell nanofibers

Wearable flexible sensors have developed rapidly in recent years because of their improved capacity to detect human motion in wide-ranging situations. In order to meet the requirements of flexibility and low detection limits, a new pressure sensor was fabricated based on electrospun barium titanate/multi-wall carbon nanotubes (BTO@MWCNTs) core-shell nanofibers coated with styrene-ethylene-butene-styrene block copolymer (SEBS). The sensor material (BTO@MWCNTs/SEBS) had a SEBS to BTO/MWCNTs mass ratio of 20:1 and exhibited an excellent piezoelectricity over a wide range of workable pressures from 1 to 50 kPa, higher output current of 56.37 nA and a superior piezoresistivity over a broad working range of 20–110 kPa in compression. The sensor also exhibited good durability and repeatability under different pressures and under long-term cyclic loading. These properties make the composite ideal for applications requiring monitoring subtle pressure changes (exhalation, pulse rate) and finger movements. The pressure sensor developed based on BTO@MWCNTs core-shell nanofibers has demonstrated great potential to be assembled into intelligent wearable devices.

Gel-sol and colorimetric dual-modal sensor for highly selective and sensitive detection of iodide ions based on gelatin fabricated AuNPs

Excessive intake or lack of iodide ions (I-) will have serious impact on human growth and health. Therefore, the highly selective and sensitive detection of I- is particularly urgent. Herein, a dual-modal sensor based on colorimetric and gel-sol signal responses has been developed for the visual detection of I-. Visual sensing based on I- triggered dual-signal simultaneous response can reduce the interference of false positive signals and improve detection accuracy. This dual-modal sensor (Gel-AuNPs) is constructed by the in situ reduction of chloroauric acid using gelatin (Gel) with unique topological structure and reduction properties to prepare gold nanoparticles (AuNPs). The presence of I- can induce a noticeable color change from red to yellow (attributed to the occurrence of redox reaction), and the selective visual detection of I- was realized in a wide concentration range with a linear fitting coefficient of 0.9983 and a limit of detection (LOD) of 30.1 μM. Simultaneously, based on the change in viscosity in the gel-sol phase transformation process (attributed to the salting-in effect of I-), the quantitative relationship of I- detection (R2 = 0.9937) was then established. Furthermore, the Gel-AuNPs hydrogel exhibited high sensitivity for detecting I- in actual water samples such as seawater and tap water. More importantly, the in situ synthesized Gel-AuNPs showed good solid-state stability and strong salt tolerance, implying the potential scope of their practical application in different harsh conditions. As such, this visual sensing system with dual signal responses will have prospective applications in detection and analysis in due course.

Neural networks based fluorescence and electrochemistry dual-modal sensor for sensitive and precise detection of cadmium and lead simultaneously

Heavy metals are harmful and it’s meaningful to achieve co-detection. In this work, fluorescence (FL) and electrochemistry (EC) dual-modal sensors combined with neural networks are proposed to detect cadmium (Cd2+) and lead (Pb2+) without pretreatment for the first time. Dual-modal sensing eliminates individual limitations of FL and EC and combines their superiority. Quantum dots and sea urchin-like FeOOH are used as sensitive materials, among which FeOOH is used for the first time to detect Pb2+ with high repeatability and sensitivity. Combining with the proposed neural networks, the mean absolute error of Cd2+ and Pb2+ predicted are 0.2176 μg/L and 0.6002 μg/L, respectively, which are far better than traditional analysis methods. The R-Squared between the predicted value and the true value is 0.974 (Cd2+) and 0.999 (Pb2+), respectively, which verifies the feasibility of the designed sensor. This model eliminates the mutual interference between Cd2+ and Pb2+ based on the synergistic effect and can be used for low-level detection in water samples with complex background. In addition, the designed model could combine with other types of sensors to accurately monitor global-local waters. It also provides new ideas for data fusion, which expands the flexibility in environmental protection and health care.

Reusable ring-like Fe3O4/Au nanozymes with enhanced peroxidase-like activities for colorimetric-SERS dual-mode sensing of biomolecules in human blood

Peroxidase−like nanozymes have led to important progress in biosensing, but most of nanozyme sensing systems are currently established by a single−signal output mode, which is susceptible to environmental and operational factors. Thus construction of a dual−signal output nanozyme sensing system is essential for obtaining reliable and robust performance. In this study, a novel peroxidase mimicking nanozyme was developed by decorating magnetic ring-like Fe3O4 with gold nanoparticles (R–Fe3O4/Au) for the colorimetric and surface-enhanced Raman scattering (SERS) dual-mode detection of biomolecules in human serum. The R–Fe3O4/Au nanozymes served as mimetic peroxidase which can catalyze the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine by hydrogen peroxide, and concomitantly as SERS substrates for detecting the Raman signals of oxidized products, providing an effective approach to investigate the reaction kinetics of enzymes. Based on the redox reactions, the nanozymes achieved colorimetric−SERS dual−mode sensing of glutathione (GSH) and cholesterol with detection limits as low as 0.10 μM and 0.08 μM, respectively. Furthermore, the nanozymes enabled rapid detection of GSH and cholesterol in serum without any complicated sample pretreatment. The R–Fe3O4/Au catalyst still displayed excellent peroxidase activity even after repeated use for 5 times. The proposed colorimetric-SERS dual-mode sensors exhibited good accuracy and reproducibility, which provides a new avenue for exploiting multifunctional sensors and has a great application prospect in biosensing.

Construction of zinc selenide microspheres decorated with octadecylamine-functionalized reduced graphene oxide as an effective catalyst for the dual-mode detection of chloroquine phosphate

Zinc selenide microspheres were constructed using a simple hydrothermal technique at 180°C. It was ultrasonically treated with reduced graphene oxide modified with octadecylamine alkyl amine to form a hybrid nanocomposite. The optical, structural, and functional analysis by ultraviolet (UV) absorbance, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the crystal nature of the microspheres and the successful formation of the nanocomposite. Field emission scanning electron microscopy and transmission electron microscopy were done to study the morphological properties of the material. It was further used to fabricate a dual-modality sensor using both electrochemical and absorbance techniques for the detection of antimalarial drug chloroquine phosphate (CQP), which was used for the treatment of COVID-19 (SARS-CoV-2) virus. For electrochemical detection, the sensor showed a very low detection limit of 1.43 nM at a linear working range of 0.199–250.06 μM and a high sensitivity of 43.912 μA/μM/cm2. For UV-based detection, the sensor showed a very low detection limit of 6.88 nM at a linear working range of 0.045–7.324 μM. The sensor showed excellent analyte recovery rate for real-time analysis in biological as well as environmental samples. The results suggested that the sensor is effective for the detection of CQP with feasibility for future commercialization.

Magnetic flexible sensor with tension and bending discriminating detection

The flexible wearable sensors with high sensitivity and stability provide wide potential in artificial intelligence and human–machine interaction. However, dual-modal sensor with contact and non-contact working mode based on a facile and cost-effective methodology which can recognize external stimulus forms remains a challenge. Especially, magnetic non-contact sensing performance has gained increasing attention in smart wearable device. This work reports a flexible and magnetic sensor based on a sandwich structure film (SSF) which can detect both tension and bending stimuli by supplementing opposite electric signal feedbacks. Notably, the ΔR/R0 of SSF sensor reaches 44.1% at 5% tensile strain and it presents excellent stability even after 10,000 cycles. Moreover, the ΔR/R0 of SSF sensor maintains at −17.2% under 2 mm bending displacement. Additionally, SSF sensor can be employed as electronic skin to perceive the human joint motion in real-time. Furthermore, the direction and density of magnetic field applied to SSF sensor can be clearly discriminated, thus a non-contact magnetic keyboard has been designed and developed. As a result, the facile manufacturing processes and outstanding multifunctional sensing characteristics endow SSF sensor with high implementation potential in the next-generation intelligent electronic equipment or systems.

Impedance-Optical Dual-Modal Cell Culture Imaging With Learning-Based Information Fusion.

While Electrical Impedance Tomography (EIT) has found many biomedicine applications, better image quality is needed to provide quantitative analysis for tissue engineering and regenerative medicine. This paper reports an impedance-optical dual-modal imaging framework that primarily targets at high-quality 3D cell culture imaging and can be extended to other tissue engineering applications. The framework comprises three components, i.e., an impedance-optical dual-modal sensor, the guidance image processing algorithm, and a deep learning model named multi-scale feature cross fusion network (MSFCF-Net) for information fusion. The MSFCF-Net has two inputs, i.e., the EIT measurement and a binary mask image generated by the guidance image processing algorithm, whose input is an RGB microscopic image. The network then effectively fuses the information from the two different imaging modalities and generates the final conductivity image. We assess the performance of the proposed dual-modal framework by numerical simulation and MCF-7 cell imaging experiments. The results show that the proposed method could improve the image quality notably, indicating that impedance-optical joint imaging has the potential to reveal the structural and functional information of tissue-level targets simultaneously.

Frequency-selective acoustic and haptic smart skin for dual-mode dynamic/static human-machine interface.

Accurate transmission of biosignals without interference of surrounding noises is a key factor for the realization of human-machine interfaces (HMIs). We propose frequency-selective acoustic and haptic sensors for dual-mode HMIs based on triboelectric sensors with hierarchical macrodome/micropore/nanoparticle structure of ferroelectric composites. Our sensor shows a high sensitivity and linearity under a wide range of dynamic pressures and resonance frequency, which enables high acoustic frequency selectivity in a wide frequency range (145 to 9000 Hz), thus rendering noise-independent voice recognition possible. Our frequency-selective multichannel acoustic sensor array combined with an artificial neural network demonstrates over 95% accurate voice recognition for different frequency noises ranging from 100 to 8000 Hz. We demonstrate that our dual-mode sensor with linear response and frequency selectivity over a wide range of dynamic pressures facilitates the differentiation of surface texture and control of an avatar robot using both acoustic and mechanical inputs without interference from surrounding noise.

Optical Microfibers for Sensing Proximity and Contact in Human-Machine Interfaces.

The monitoring of proximity-contact events is essential for human-machine interactions, intelligent robots, and healthcare monitoring. We report a dual-modal sensor made with two functionalized optical microfibers (MFs), which is inspired by the somatosensory system of human skin. The integrated sensor with a hierarchical structure gradationally detects finger approaching and touching by measuring the relative humidity (RH) and force-triggered light intensity variations. Specifically, the RH sensory part shows enhanced evanescent absorption, achieving a sensitive RH measurement with a fast response (110 ms), a high resolution (0.11%RH), and a wide working range (10-100%RH). Enabled by the transition from guided modes into radiation modes of the waveguiding MF, the force sensory part exhibits a high sensitivity (6.2%/kPa) and a fast response (up to 1.5 kHz). By using a real-time data processing unit, the proximity-contact sensor (PCS) achieves continuous detection of the full-contact events, including finger approaching, contacting, pressing, releasing, and leaving. As a proof of concept, the electromagnetic-interference-free PCS enables a smart switch system to recognize the proximity and contact of bare/gloved fingers. Moreover, skin humidity detection and respiration monitoring are realized. These initial results pave the way toward a category of optical collaborative devices ranging from human-machine interfaces to multifunctional on-skin healthcare sensors.

Tough and extremely temperature-tolerance nanocomposite organohydrogels as ultrasensitive wearable sensors for wireless human motion monitoring

MXenes have attracted great attention due to their multifunctional properties and abundant surface terminations. However, it remains a considerable challenge to construct MXene hydrogels with high toughness and long-term sensory performance to withstand harsh environments. Herein, a multifunctional conductive organohydrogel based on 2D MXene nanosheets and ZA fibers were fabricated and then assembled wireless wearable sensors to track human movement. By introducing ternary mixture, the organohydrogels possess ultra-low temperature resistance (−81 °C) and moisture retention. Simultaneously, the interaction of alginate chains induced by Zn ions with PAM endows the organohydrogels with superior mechanics. Amazingly, the hydrogel sensor exhibited the highest pressure sensing performance (Sp1 = 782.7 kPa−1) and harsh-environment tolerance. Importantly, zinc-activated MXene nanosheet endowed the resultant with the favorable antibacterial ability and serves in organohydrogels for potential medical applications. This method provides a facile approach for designing sustainable dual-mode sensors with high toughness, antibacterial performance, all-weather availability, and wireless transmission.

“Off-on” fluorescence probe based on green emissive carbon dots for the determination of Cu2+ ions and glyphosate and development of a smart sensing film for vegetable packaging

An ultra-sensitive glyphosate nanosensor, based on carbon dots (CDs), was successfully developed with excellent long-wavelength emission (530 nm), a high quantum yield (41.3%), and an impressive detection limit (0.8 ng·mL−1). This is the lowest value for glyphosate detection achieved by CD-based fluorescence analysis. The sensor was derived from a separate precursor, 1,4-dihydroxyanthraquinone, and was based on the “off-on” fluorescence analysis, where Cu2+ acts as a dynamic quencher and glyphosate as a fluorescence restorer (excitation wavelength 460 nm). Trace detection of glyphosate is possible with a wide detection range of 50–1300 ng·mL−1 and spiked recoveries between 93.3 and 110.0%. Exploration in depth confirmed that (1) the fluorescence of CDs was derived from the carbon core, (2) the large sp2 conjugated domain consisting of graphitic carbon and nitrogen contributed to the long-wavelength emission, and (3) CDs had an impressive binding interaction with Cu2+, which endow high sensitivity to glyphosate detection. The nanosensor has also be used as a dual-mode visual sensor and a smart sensing membrane that can identify glyphosate on the surface of vegetables, thus showing good practical applicability.Graphical abstract Synthetic methods of G-CDs and its detection mechanisms for glyphosate.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00604-022-05241-5.

Sustainable and Green Synthesis of Waste-Biomass-Derived Carbon Dots for Parallel and Semi-Quantitative Visual Detection of Cr(VI) and Fe3.

Carbon dot (CD)-based multi-mode sensing has drawn much attention owing to its wider application range and higher availability compared with single-mode sensing. Herein, a simple and green methodology to construct a CD-based dual-mode fluorescent sensor from the waste biomass of flowers of wintersweet (FW-CDs) for parallel and semi-quantitative visual detection of Cr(VI) and Fe3+ was firstly reported. The FW-CD fluorescent probe had a high sensitivity to Cr(VI) and Fe3+ with wide ranges of linearity from 0.1 to 60 µM and 0.05 to 100 µM along with low detection limits (LOD) of 0.07 µM and 0.15 µM, respectively. Accordingly, the FW-CD-based dual-mode sensor had an excellent parallel sensing capacity toward Cr(VI) and Fe3+ with high selectivity and strong anti-interference capability by co-using dual-functional integration and dual-masking strategies. The developed parallel sensing platform was successfully applied to Cr(VI) and Fe3+ quantitative detection in real samples with high precision and good recovery. More importantly, a novel FW-CD-based fluorescent hydrogel sensor was fabricated and first applied in the parallel and semi-quantitative visual detection of Cr(VI) and ferrous ions in industrial effluent and iron supplements, further demonstrating the significant advantage of parallel and visual sensing strategies.

Field-Effect Transistor with a Plasmonic Fiber Optic Gate Electrode as a Multivariable Biosensor Device.

A novel multivariable system, combining a transistor with fiber optic-based surface plasmon resonance spectroscopy with the gate electrode simultaneously acting as the fiber optic sensor surface, is reported. The dual-mode sensor allows for discrimination of mass and charge contributions for binding assays on the same sensor surface. Furthermore, we optimize the sensor geometry by investigating the influence of the fiber area to transistor channel area ratio and distance. We show that larger fiber optic tip diameters are favorable for electronic and optical signals and demonstrate the reversibility of plasmon resonance wavelength shifts after electric field application. As a proof of principle, a layer-by-layer assembly of polyelectrolytes is performed to benchmark the system against multivariable sensing platforms with planar surface plasmon resonance configurations. Furthermore, the biosensing performance is assessed using a thrombin binding assay with surface-immobilized aptamers as receptors, allowing for the detection of medically relevant thrombin concentrations.

Intelligently design primary aromatic amines derived carbon dots for optical dual-mode and smartphone imaging detection of nitrite based on specific diazo coupling

Primary aromatic amines derived carbon dots (PAA-CDs) with the protonated amino groups and high quantum yield of 46% were favorably obtained by one-step solvothermal treatment of m-phenylenediamine (m-PDA) in acidic environment. The interaction between the PAA-CDs and nitrite (NO2-) was inherited the characteristic reaction of m-PDA (a primary aromatic amine) and NO2-, resulting in strong fluorescence quenching and obvious absorption variation of the PAA-CDs. Meanwhile, a chromogenic reaction of diazo coupling can cause significant color changes. Hence, the PAA-CDs were developed for an optical dual-mode and smartphone imaging sensor for NO2- detection in the range of 3.0 ~ 40.0 μM with high selectivity, good sensitivity, and excellent anti-interference capability. A limit of detection (LOD) of 0.024 μM and 0.16 μM was implemented by fluorometry and colorimetry, respectively. For smartphone imaging colorimetry, the LODs of 0.46 μM (visible color) and 0.99 μM (fluorescence color) were acquired. More importantly, the established sensor has been successfully applied for the dynamic detection of NO2- in various food samples with the satisfying results. A smartphone imaging colorimetry method based on the CDs was firstly proposed to visually and quantitatively detect NO2-, which will broaden the application range of the CDs in food safety inspection.