Artificial intelligence-integrated smartphone-based handheld detection of fluoride ion by Al3+-triggered aggregation-induced red-emssion enhanced carbon dots

Dual-mechanism detecting fluoride and tetracycline in food matrices using red-emitting carbon dots

Excessive exposure to fluoride and tetracycline can cause severe dental damage, including tetracycline-induced tooth discoloration and dental fluorosis. Herein, we introduce a dual-mechanism sensing strategy using red-emitting carbon dots (R-CDs) for the independent detection of fluoride and tetracycline. A key advantage of R-CDs as sensors is their ability to selectively identify both analytes through long-wavelength emission with a large Stokes shift. For fluoride detection, we developed a fluorescence-enhanced sensor based on R-CDs-Fe3+ via a competitive binding mechanism. Meanwhile, tetracycline detection was achieved using a fluorescence-quenching sensor leveraging static quenching and the internal filter effect (IFE). The successful quantification of fluoride and tetracycline in food matrices demonstrates the practical potential of R-CDs in food safety monitoring. Additionally, this study presents a novel framework for designing multi-target detection systems using a single type of carbon dots across different sensing mechanisms.

Carboxyl and carbonyl groups of carbon dots co-coordinated assembly with Al3+ to emission-enhanced aggregates for sensitive sensing and efficient removal

It is very challenging to prepare carbon dots (CDs) with aggregation-induced emission (AIE) property for simultaneous sensitive sensing and efficient removal. Herein, blue-emission CDs were facilely prepared by one-step solvothermal treatment of vine tea. Optical characterizations demonstrated that AIE phenomenon of CDs came from the restricted intramolecular motion. Through selected chemical modifications for structure-property relationship analysis, carboxyl and carbonyl groups on CDs were demonstrated as co-coordination active sites to bind with Al3+ for turn-on sensing process. Fluorescence enhancement of CDs by Al3+ chelation could be attributed to synergistic mechanism of AIE and chelation-enhanced fluorescence. Thus, the prepared CDs has been used as a selective, sensitive, and effective fluorescent probe for fast Al3+ sensing (response time, 5 min; linear range, 0.5-30.0 μM; limit of detection, 0.31 μM). More interestingly, high binding affinity between CDs and Al3+ made them assembly into large aggregates via flocculation for Al3+ removal (removal efficiency, 97.5 %) with extraordinary adsorption behavior (adsorption capacity, 1316 mg/g). Furthermore, the proposed CDs were successfully applied in detecting Al3+ in real wastewater samples with acceptable recoveries (98.7-103.0 %) and superior precision (relative standard deviations, less than 3.82 %), and removing Al3+ in spiked samples with satisfactory results. The work thus gives a demonstration of the potential fabrication of CDs with AIE property, and a better understanding of sensing and removal mechanisms for more rational design of CDs with application values.

Hydrothermal Synthesis of Nitrogen-Doped Carbon Dots for Selective Fe3+ Detection

Carbon dots (CDs) have recently regarded as an attractive fluorescent sensor for water quality detection. However, the actual detection application of CDs is limited owing to the low fluorescence quantum yield (QY) and unclear ion detection mechanism. Here, nitrogen doped CDs (N-CDs) with abundant amide groups, which were easy to prepare using urea and citric acid under mild reaction conditions and displayed great light absorption and strong fluorescence performance with a fluorescence QY of up to 26.6%. More importantly, N-CDs could achieve selective detection of iron ion (Fe3+) and its concentrations as low as 0.47 µM in water. Meanwhile, N-CDs exhibited a good linear relationship within the concentration range of 0.5-500 µM of Fe3+. This mainly because the introduction of amide groups of N-CDs not only could serve as both donors (NH-), but also acceptors (C = O) for hydrogen bonding, which consequently increased multifunctional fluorescent recognition sites and formed coordination interactions with metal ions, and ultimately achieved fluorescence detection of ions. Therefore, the preparation of N-CDs rich in amide groups provides a promising strategy for rapid and efficient detection of Fe3+ ions for water quality detection applications.

Carbon dot-based fluorescent sensor for selective and sensitive detection of persulfate

Persulfate, a powerful oxidizing agent, is extensively employed in numerous industries. Accurate and rapid detection of persulfate (S2O8 2-) is essential. This study reports the development of a fluorescent sensor based on Am-CDs. It is synthesized from ascorbic acid (AA) and m-phenylenediamine (m-PD) through a one-step hydrothermal method. The fluorescence of Am-CDs demonstrated selective sensitivity to S2O8 2- via static quenching. A sensitive fluorescent sensor was constructed for S2O8 2-, exhibiting a linear detection range of 1.96 to 15.59 μM with a limit of detection (LOD) of 0.94 μM. This fluorescence method was successfully applied to detect S2O8 2- in water samples, achieving recoveries of 98.07% to 102.33%. The fluorescent sensor developed in this study offers a simple and effective method for quantifying S2O8 2- in aquatic environments.

Combining digital imaging and quantum dots for analytical purposes

This review provides a critical assessment of the most recent advances in digital imaging (DI) methods, applied for the development of analytical methodologies combining quantum dots (QDs). The state-of-the-art, treatment of data, instrumental considerations, software, sensing approaches, and optimization of the resulting methods are reported. Applications of the technology for the analysis of food and beverages, biomedically relevant analytes, drugs, environmental samples and forensic samples are also discussed. These examples aim to highlight the advantages of DI over traditional instrumentation, that in combination with QDs represents a powerful option for low-cost and on-site analyses. Moreover, some of these DI methods have been explored in the context of green chemistry principles, demonstrating a sustainable approach to modern analytical challenges.

Carbon dots-based dual-mode sensor for highly selective detection of nitrite in food substrates through diazo coupling reaction

As an antioxidant and preservative agent, nitrite (NO2-) plays an essential role in the food industry to maintain freshness or inhibit microbial growth. However, excessive addition of NO2- is detrimental to health, so accurate and portable detection of NO2- is critical for food quality control. Notably, the selectivity of most carbon dots (CDs)-based fluorescence sensors was not enough due to the nonspecific interaction mechanism of hydrogen bond, electrostatic interaction and inner filter effect etc. Herein, a novel fluorescence/UV-vis absorption (FL/UV-vis) dual-mode sensor was developed on basis of mC-CDs, which were prepared by simple solvothermal treatment of m-Phenylenediamine (m-PDA) and cyanidin cation (CC). The fluorescence of these mC-CDs could be selectively responded by NO2- through the specific diazo coupling reaction between NO2- and amino groups on the surface of mC-CDs, thus effectively improving the selectivity of NO2- detection. The CDs-based fluorescence sensor possessed a low detection limit of 0.091 μM and 0.143 μM for FL and UV-vis methods and the excellent linear range of 0.0-60.0 μM. Furthermore, the mC-CDs sensor was employed to detect NO2- in real samples with a recovery rate of 97.11 %-104.15 % for quantitative addition. Moreover, the smartphone-assisted fluorescence sensing platform developed could identify the subtle color changes that could not be distinguished by the naked eye, and had the advantages of fast detection speed and intelligence. More importantly, the portable solid phase sensor based on mC-CDs had been successfully applied to the specific fluorescence identification and concentration monitoring of NO2-. Accordingly, the designed sensor provided a new strategy for the highly selective and convenient sensing of NO2- in food substrates, and paved the way for the wide application of CDs-based nanomaterials in the detection of food safety.

Smartphone-assisted hydrogel sensing platform based on double emission carbon dots for portable on-site tetracycline detection

Innovative double-emission carbon dots (DE-CDs) were synthesized via a one-step hydrothermal method using fennel and m-phenylenediamine (m-PD) as precursors. These DE-CDs exhibited dual emission wavelengths at 432 and 515 nm under different excitations, making them highly versatile for fluorescence-based applications. The fluorescence of the DE-CDs was efficiently quenched by tetracycline (TC) through the inner filter effect (IFE), allowing for the construction of a sensitive dual-response fluorescent sensor. This sensor demonstrated a strong exponential correlation with TC concentrations in the range 0.99-118 μM, achieving a low detection limit of 53.4 nM, which is appropriate for environmental monitoring. To further enhance its practicality, a smartphone-integrated fluorescent hydrogel film sensing platform was developed. This portable and user-friendly system enabled rapid, on-site TC detection in water samples, combining high sensitivity with convenience for real-world applications. The integration of the DE-CD-based sensor into a hydrogel platform addressed the challenge of translating laboratory precision into field-ready tools. This study revealed the potential of DE-CDs as a robust and efficient solution for bridging the gap between laboratory-based analysis and portable, on-site environmental monitoring.

Flexible, self-healing and portable supramolecular visualization smart sensors for monitoring and quantifying structural damage

Visually monitoring micro-crack initiation and corrosion failure evolution is crucial for early diagnosis of structural health and ensuring safe operation of infrastructures. However, existing damage detecting approaches are subject to the limited-detection of heterogeneous structures, intolerance of harsh environments, and challenge of quantitative analysis, impeding applications in structural health monitoring (SHM). Herein, we present a stretchable, semi-quantitative, instrument-free, supramolecular SHM sensor by integrating a polyurea elastomer with sensitive corrosion-probes, enabling localized corrosion monitoring and quantification of failure dynamics. Initially, a correlation between visual monitoring signals and structural health status is proposed, and sensor-based image processing software that accurately quantifies structural failure indicators (crack scale, corrosion reactivity and deterioration status) is proposed. Moreover, this sensor can be fabricated as multiple derivatives: a coating or patch covered on metallic substrates and an ionic-responsive test strip, ensuring real-time detection of the initiation of pitting, degradation events of metallic components and convenient monitoring of ion concentrations in corrosive media. Furthermore, the inherent geometric plasticity and dynamic hydrogen-bonded network validates the reliability for heterogeneous components and stability under extreme environments of sensors. This portable, smart SHM strategy established the channel-transformation model from corrosion dynamics to visual signals, exhibiting prospects for structural monitoring in offshore energy-harvesting equipment.

Modulating carbon dots from aggregation-caused quenching to aggregation-induced emission and applying them in sensing, imaging and anti-counterfeiting

Aggregation Induced Emission Carbon Dots (AIE-CDs) address the problem of conventional CDs being quenched in the solid-state. However, there are still challenges in comprehending the luminescence mechanism. This work proposed a strategy for preparing green, yellow, and near-infrared CDs by modifying the functional groups on the precursor from hydroxyl and amino to p-methylenediamine, in which electronic supply capacity determined the redshift. Additionally, The CDs' properties transformed from Aggregation-Caused Quenching (ACQ) to AIE was realized by substituting non-rotatable hydroxyl or amino groups with the rotatable p-methylenediamine on the precursor. The resulting CDs were then applied in multifield. C-CDs was used for ratiometric detection of Al3+ and F- in pure water through three methods including fluorometer, test strip and smartphone. R-CDs was used for imaging cell nucleus and zebrafish. NIR-CDs (λem = 676 nm) exhibits dual emission, AIE and phosphorescent characteristics was used for triple anti-counterfeiting and binary information encryption. In summary, our finding presented a strategy for preparing multicolor CDs, proposed a mechanism for the transition of CDs from ACQ to AIE, and explore their multiple applications in anti-counterfeiting, information encapsulation, sensing and imaging.

Controllable fabrication of high-quantum-yield bimetallic gold/silver nanoclusters as multivariate sensing probe for Hg2+, H2O2, and glutathione based on AIE and peroxidase mimicking activity

The grave threat posed by heavy metals and food hazards has increased the urgency of rapid and precise detection for food security and human health. Efficient multivariate sensing probes are imperatively required for sensing heavy metals and tumor markers, which are still facing great challenge in terms of multi-functional integration. Here, bimetallic gold-silver nanoclusters (NG-AuAgNCs) were developed with unique aggregation-induced-emission (AIE) property and peroxidase (POD) mimicking activity towards the efficient multivariate sensing via optimization of the precursors. The NG-AuAgNCs emitted at 614 nm and enable AIE feature with lifetime of 12.61 μs and high quantum yield of 40.5%. Possessing AIE and POD activity, the NG-AuAgNCs show great potential as fluorimetric and colorimetric dual-mode probe for multivariate sensing Hg2+, H2O2 and GSH, with good recoveries in real samples. The NG-AuAgNCs paper sensors further integrating with smartphone, achieved portable detection of Hg2+ with limit of detection (LOD) of 19 nM, while the colorimetric-mode presented consecutive response to H2O2 and GSH via a reversible oxidase tetramethylbenzidine process with LODs of 7.02 and 0.45 μM, respectively. This work not only demonstrates a multivariate probe for environment and human health, but also provides valuable insights for the function integration of the nanocluster via synthetic manipulation.

An artificial intelligence handheld sensor for direct reading of nickel ion and ethylenediaminetetraacetic acid in food samples using ratiometric fluorescence cellulose paper microfluidic chip

User-friendly in-field sensing protocol is crucial for the effective tracing of intended analytes under less-developed countries or resources-limited environments. Nevertheless, existing sensing strategies require professional technicians and expensive laboratory-based instrumentations, which are not capable for point-of-care on-site analyses. To address this issue, artificial intelligence handheld sensor has been designed for direct reading of Ni2+ and EDTA in food samples. The sensing platform incorporates smartphone with machine learning-driven application, 3D-printed handheld device, and cellulose paper microfluidic chip stained with ratiometric red-green-emission carbon dots (CDs). Intriguingly, Ni2+ introduction makes green fluorescent (FL) of CDs glow but red FL fade because of the coordination of Ni2+ with CDs verified by density functional theory (DFT), concurrently manifesting continuous FL colour transition from red to green. Subsequent addition of EDTA renders FL of CDs-Ni2+ recover owing to the capture of Ni2+ from CDs by EDTA based on strong chelation effect of EDTA on Ni2+ confirmed via DFT, accompanying with a noticeable colour returning from green to red. Inspired by above FL phenomena, CDs-based cellulose paper microfluidic chips are first fabricated to facilitate point-of-care testing of Ni2+ and EDTA. Designed fully-automatic handheld sensor is utilized to directly output Ni2+ and EDTA concentration in water, milk, spinach, bread, and shampoo based on wide linear ranges of 0-48 μM and 0-96 μM, and low limits of detection of 0.274 μM and 0.624 μM, respectively. The proposed protocol allows for speedy straightforward on-site determination of target analytes, which will trigger the development of automated and intelligent sensors in near future.

A cotton swab platform for fluorescent detection of aluminum ion in food samples based on aggregation-induced emission of carbon dots

A novel portable cotton swab based on nitrogen-doped carbon dots (NCDs) for Al3+ detection was constructed for the first time. NCDs with bright green fluorescence were prepared by hydrothermal method with phenylhydrazine hydrochloride and 3-hydroxy-2-naphthoic acid hydrazide as precursors. The surface of NCDs was exposed to abundant functional groups (such as amino, carboxyl, hydroxyl, etc.), which was helpful for the formation of complexes between NCDs and Al3+. In the presence of Al3+, the aggregation of NCDs obviously induced their fluorescence enhancement due to the aggregation-induced emission (AIE) of NCDs. Furthermore, the quantum yield (QY) of NCDs was enhanced by 12 times with Al3+, and the fluorescence lifetime was increased by 7.54 ns. The fluorescence intensity was linearly correlated with the concentration of Al3+ (2.5-300 μM), and the limit of detection was 0.76 μM. Moreover, for the portable way, cotton swabs were successfully employed to construct the sensors for the detection of Al3+ in food samples. This proposal has potential for the application in food analysis.

A sharp and selective fluorescence paper-based sensor based on inner filter effect for ratiometric detection of four Sudan dyes in food matrix

The addition of Sudan dyes with carcinogenic effects to food threatens human health. Herein, a ratiometric fluorescence strip consisting of core-shell upconversion particles (NaYF4:Yb,Tm@NaYF4:Yb,Er), metal-organic frameworks and dual-template molecularly imprinted polymers was developed to selectively and sensitively detect four Sudan dyes based on inner filter effect (detection time only takes 8 min). The high adsorption capacity of metal-organic frameworks and the greater overlap between the emission of NaYF4:Yb,Tm@NaYF4:Yb,Er and the absorbance of four Sudan dyes enable the signal responses to be more sensitive. The limits of detection in chilli powder samples are as low as 29.87 ng/g, 37.55 ng/g, 47.89 ng/g and 51.02 ng/g, with satisfactory recovery (93.32-103.4%) and minor relative standard deviations (≤4.3%). This method broadens the idea for low-cost and portable detection of multiple illegal additives in complex substrates with high selectivity and sensitivity based on one kind of fluorescent strip.

Smartphone-based sensing and in vivo and in vitro imaging of Mn(VII) based on nitrogen-doped red fluorescent carbon dots

Smartphone-assisted visual assay platform provides novel insight for the real-time in-field quantitation of intended analytes in resource-insufficient areas. Herein, nitrogen-doped red fluorescent (FL) carbon dots (R-CDs) were developed for the timely on-site quantitation of Mn(VII) using the smartphone-assisted assay platform. R-CDs, possessing a desirable bright red FL at 616 nm under a 470 nm excitation, were fabricated through hydrothermal treatment adopting passion fruit and neutral red as precursors. Interestingly, bright red FL at 616 nm are gradually quenched upon introducing Mn(VII) based on the inner filter effect, concurrently accompanying with significant FL color variation from bright red to dark red. Inspired by the above-mentioned phenomena, hue-saturation-values (HSV) of real-time captured images could be precisely quantified through a color recognition APP within the smartphone, of which the V/S values could be employed to quantify Mn(VII) with a linear range of 50-400 μM. Furthermore, confocal fluorescence imaging of HeLa cells and zebrafish larvae demonstrates that R-CDs could be employed for the visual determination of Mn(VII) in vivo and in vitro, illustrating that R-CDs possess powerful practical application prospect in biosystem.

N-doped carbon dots for the determination of Al3+ and Fe3+ using aggregation-induced emission

New portable hydrogel sensors for Al3+ and Fe3+ detection were designed based on the aggregation-induced emission (AIE) and color change of N-doped carbon dots (N-CDs). N-CDs with yellow fluorescence were prepared by a one-pot hydrothermal method from 2,5-dihydroxyterephthalic acid and acrylamide. The fluorescence of N-CDs was enhanced by Al3+ about 20 times and quenched by Fe3+. It was interesting that although Fe3+ showed obvious quenching on the fluorescence of N-CDs it did not cause a noticeable change in the fluorescence of N-CDs + Al3+. The colorless solution of N-CDs appeared blue in the presence of Fe3+ without the influence of Al3+. Therefore, the turn-on fluorometry and colorimetry systems based on N-CDs were constructed for the simultaneous detection of Al3+ and Fe3+. Furthermore, the portable sensing of Al3+ and Fe3+ was realized with the assistance of hydrogel, filter paper, cellulose acetate, and cellulose nitrate film. The proposed approach was successfully applied to the detection of Al3+ and Fe3+ in food samples and cell imaging.

Aqueous Solution Enhanced Room Temperature Phosphorescence through Coordination-Induced Structural Rigidity

Achieving aqueous solution enhanced room temperature phosphorescence (RTP) is critical for the applications of RTP materials in solution phase, but which faces a great challenge. Herein, for the first time, a strategy of coordination-induced structural rigidity is proposed to achieve enhanced quantum efficiency of aluminum/scandium-doped phosphorescent microcubes (Al/Sc-PMCs) in aqueous solution. The Al/Sc-PMCs in a dry state exhibit a nearly invisible blue RTP. However, they emit a strong RTP emission in aqueous solution with a RTP intensity increase of up to 22.16-times, which is opposite to common solution-quenched RTP. The RTP enhancement mechanism is attributed to the abundant metal sites (Al3+ and Sc3+ ions) on the Al/Sc-PMCs surface that can tightly combine with water molecules through the strong coordination. Subsequently, these coordinated water molecules as the bridging agent can bind with surface groups by hydrogen bonding interaction, thereby rigidifying chemical groups and inhibiting their motions, resulting in the transition from the nonradiative decay to the radiative decay, which greatly enhances the RTP efficiency of the Al/Sc-PMCs. This work not only develops a coordination rigidity strategy to enhance RTP intensity in aqueous solution, but also constructs a phosphorescent probe to achieve reliable and accurate determination of analyte in complex biological matrices.

Current trends in digital camera-based bioassays for point-of-care tests

Point-of-care and bedside tests are analytical devices suitable for a growing role in the current healthcare system and provide the opportunity to achieve an exact diagnosis by an untrained person and in various conditions and sites where it is necessary. Using a digital camera integrated into a well-accessible device like a smartphone brings a new way in which a colorimetric point-of-care diagnostic test can provide unbiased data. This review summarizes basic facts about the colorimetric point-of-care tests, principles of how to use a portable device with a camera in the assay, applications of digital cameras for the current tests, and new devices described in the recent papers. An overview of the recent literature and a discussion of recent developments and future trends are provided.

Rapid Pathogen Purge by Photosensitive Arginine-Riboflavin Carbon Dots without Toxicity

Photo-activatable antipathogenic carbon dots (CDs) were prepared by carbonization of citric acid and arginine (Arg) via 3 min microwave treatment for use in the eradication of common microorganisms. Nitrogen-doped Arg CDs were spherical in shape with a size range of 0.5 to 5 nm. The Arg CDs were modified with fluorescent dyes, such as fluorescein sodium salt (FSS, as Arg-FSS) and riboflavin (RBF, as Arg-RBF), to improve antimicrobial potency by enhancing their application in photodynamic therapy. The modified Arg CDs afforded fluorescence emission properties at 520 nm in the green region in addition to excellent blue fluorescence intensity at 420 nm under 345 nm excitation upon their FSS and RBF conjugation, respectively. Although the cytotoxicity of Arg CDs was decreased for Arg-RBF CDs to 91.2 ± 0.7% cell viability for fibroblasts, the Arg-based CDs could be safely used for intravenous applications at 1000 μg/mL concentration. The Arg CDs showed broad-spectrum antimicrobial activity against common pathogens and the minimum inhibitory concentration of Arg CDs was almost two-fold decreased for the modified forms without UV light. However, faster and more effective antibacterial activity was determined for photosensitive Arg-RBF CDs, with total bacterial eradication upon UV-A light exposure for 30 min.