Blue Carbon Dots Research Articles

An all-in-one smartphone-assisted ratiometric fluorescent device for visual and quantitative detection of glutathione

The daily consumption of foods abundant in Glutathione (GSH) can be supplemented to maintain the homeostasis of GSH in human health and alleviate pathologies resulting from abnormal GSH levels. The fluorescence-based visual determination of GSH has gradually attracted the attention of researchers due to its robust performance and versatile implementation. However, the current GSH visual strategy primarily relies on variations in fluorescence intensity at a single emission wavelength, which poses challenges for naked-eye and portable readout, as well as distorted signals caused by complex matrix effects in real samples. Herein, a ratiometric fluorescence sensor based on carbon dots (CDs) combined with an all-in-one 3D-printed smartphone-based device was successfully developed for low-cost, visual and rapid detection of GSH without the need for an external excitation light source. The ratiometric fluorescent materials were synthesized by conjugating blue carbon dots (B-CDs) with yellow carbon dots (Y-CDs) through the utilization of selected Cu2+ ions. The resulting mechanism demonstrated that the coordination interaction between Cu2+ and residual aromatic amino groups in Y-CDs (Y-CDs-Cu2+) contributed to a newly emitted peak at 580 nm, thereby inducing fluorescence resonance energy transfer from B-CDs to Y-CDs-Cu2+. A linear correlation was found between GSH concentrations and R/B values in the range of 10–100 μM, with a limit of detection observed at 4.8 μM. By utilizing this portable device in combination with RGB analysis, the quantitative detection of GSH can be achieved even in complex food matrices such as tomatoes and grapes. The universality of this all-in-one device was further validated by pre-spraying CDs onto a paper strip for visual measurement of GSH. This work offers a portable, visual, and accessible approach to evaluating food safety and nutrition, thereby demonstrating significant economic value and holding profound implications for human health.

Enhancing Magnetic Micro- and Nanoparticle Separation with a Cost-Effective Microfluidic Device Fabricated by Laser Ablation of PMMA.

Superparamagnetic iron oxide micro- and nanoparticles have significant applications in biomedical and chemical engineering. This study presents the development and evaluation of a novel low-cost microfluidic device for the purification and hyperconcentration of these magnetic particles. The device, fabricated using laser ablation of polymethyl methacrylate (PMMA), leverages precise control over fluid dynamics to efficiently separate magnetic particles from non-magnetic ones. We assessed the device's performance through Multiphysics simulations and empirical tests, focusing on the separation of magnetite nanoparticles from blue carbon dots and magnetite microparticles from polystyrene microparticles at various total flow rates (TFRs). For nanoparticle separation, the device achieved a recall of up to 93.3 ± 4% and a precision of 95.9 ± 1.2% at an optimal TFR of 2 mL/h, significantly outperforming previous models, which only achieved a 50% recall. Microparticle separation demonstrated an accuracy of 98.1 ± 1% at a TFR of 2 mL/h in both simulations and experimental conditions. The Lagrangian model effectively captured the dynamics of magnetite microparticle separation from polystyrene microparticles, with close agreement between simulated and experimental results. Our findings underscore the device's robust capability in distinguishing between magnetic and non-magnetic particles at both micro- and nanoscales. This study highlights the potential of low-cost, non-cleanroom manufacturing techniques to produce high-performance microfluidic devices, thereby expanding their accessibility and applicability in various industrial and research settings. The integration of a continuous magnet, as opposed to segmented magnets in previous designs, was identified as a key factor in enhancing magnetic separation efficiency.

Multi-deformable interpenetrating network thermosensitive hydrogel fluorescent device for real-time and visual detection of nitrite

Functionalized thermosensitive hydrogel materials exhibit excellent properties for the fabrication of sensing devices that enable real-time visual detection of food safety duo to their good plasticity and powerful loading capacity. Here, a ratiometric fluorescent device based on an interpenetrating network (IPN) thermosensitive hydrogel was designed to embed functionalized Au nanoclusters (Au NCs) and Blue Carbon dots (BCDs) composites in a multi-network structure to build a sensitive hazardous material nitrite (NO2-) chemsensor. The hydrogel was utilized poloxamer 407 (P407), lignin and cellulose to form stable IPN structure, which resulted in complementation and synergy, thereby strengthening its porous network structure. The combination of fluorescent nanoprobes with the porous network structure has the potential to enhance stable fluorescence signals and improve sensing sensitivity. Moreover, the thermosensitive liquid-solid transition characteristics of the hydrogel facilitate its preparation into diverse sensing devices following curing at room temperature. The hydrogel device, when combined with a smartphone system, converted image information into data information, thereby enabling the accurate quantification of NO2- with a detection limit of 9.38 nM in 2 s. The designed multi-functional hydrogel device is capable of real-time differentiation of NO2- dosage with the naked eye, offering a high-contrast, rapid-response sensing methodology for visual assessment of food freshness. This research contributes to the expansion of hydrogel materials applications and the detection of hazardous materials in food safety.

Nanostructured rhodamine B/aluminosilicate extracted sugarcane bagasse modified with tobacco-derived carbon quantum dot as ratiometric fluorescence probe for determination of tetracycline

Tetracycline (TC), as a widely used antibiotic, is very useful in treating bacterial infections. However, its residues in animal foodstuffs can enter the human body through the food cycle and causes severe and chronic diseases. On the other hand, due to its weak non-biodegradability, it is considered a threat to the environment. In this regard, the development of sensing methods to detect and measure TC is need of the hour. Herein, a dual-emission fluorescence sensor based on porous aluminosilicate structure (ASS) with rough surface hexagonal shape morphology and pore diameter less than 2 nm was prepared. The porous AAS was modified by post-modification method with blue carbon dots (CDT) and rhodamine B (RB) as two fluorophores to develop the ratiometric fluorescence (RF) sensor (CDT-AAS/RB). Nanostructured CDT-AAS/RB emitted two resolved peaks at 445 and 585 nm , which were dramatically quenched in the presence of TC. The RF sensor, with excellent sensitivity, was able to measure TC over the linear range of 0.001–150 μM with a limit of detection of 5.4 nM in the aqueous phosphate buffer. Moreover, the AAS component granted high selectivity and anti-interference ability to the sensor. In addition, the stability of the sensor was greatly improved due to the non-accumulation of CDT nanoparticles and RB molecules in the presence of the AAS. The proposed method was able to determine TC in complex real samples with satisfactory recovery, and the obtained results were validated with standard high-performance liquid chromatography technique.

Portable tri-color ratiometric fluorescence paper sensor for intelligent visual detection of dual-antibiotics and aluminium ion

The toxicological effect between co-existed antibiotics and metal ions was dangerous to the ecological environment and public health. However, the rapid quantification tools with convenience, accuracy and low cost for the detection of multiple targets were still challenging. Herein, a portable tri-color ratiometric fluorescence paper sensor was constructed by coupling of blue carbon dots and fluorescence imprinted polymer for down/up conversion simultaneous detection of tetracycline and sulfamethazine. Interestingly, the cascade detection of aluminum ion was also realized based on the individual detection system of tetracycline without the assistance of complex coupling reagents. The detection limits of smartphone method for the visual detection of tetracycline, sulfamethazine and aluminum ion were calculated as 0.014 μM, 0.004 μM and 0.019 μM, respectively. The portable fluorescence paper sensor was applied for the visual detection of tetracycline, sulfamethazine and aluminum ion in actual samples successfully with satisfactory recoveries. With the advantages of rapidness, low cost, and portability, the developed portable fluorescence paper sensor provided a new strategy for the visual real-time detection of multiple targets.

One-step microwave synthesis of high-efficiency solid-state luminescent carbon dots with aggregation-induced emission

Carbon dots (CDs) are biophilic quantum dots with excellent luminescent properties, however, the aggregation-caused quenching (ACQ) effect is a serious limitation for their application in solid-state devices. In this manuscript, a solid-state luminescent blue CDs (B-CDs) with a high fluorescence quantum yield of 52% was prepared by a microwave-assisted method. The B-CDs showed weak fluorescence and with a photoluminescence fluorescence quantum yield (PLQY) of only 0.63% in aqueous solution, but exhibited an aggregation-induced emission in the solid state. The AIE phenomenon of B-CDs was shown to result from the inhibition of surface chromophore motion during aggregation by characterizing the PL intensity under different ratios of DCM (poor solvent). Furthermore, the fluorescence kinetic mechanism associated with the B-CDs was investigated by the time-resolved PL. Finally, a blue LED with CIE coordinates of (0.15, 18) was fabricated using B-CDs as the phosphor, showing a promising potential application in solid-state optoelectronic devices.

Enzyme-free ratiometric fluorescence and colorimetric dual-signal determination of glyphosate based on copper nanoclusters (ZIF/CuNCs) combined with blue carbon dots (bCDs)

A novel ratio fluorescent and colorimetric dual-signal sensing platform for detecting glyphosate based on blue carbon dots (bCDs) combined with ZIF/CuNCs nanomaterials that encapsulate copper nanoclusters (CuNCs) in a metal-organic framework (MOF). In principle, the immobilization of Cu2+ in ZIF/CuNCs results in complexation with imidazole in ZIF, leading to fluorescence quenching of ZIF/CuNCs, while the reference fluorophore bCDs remains unaffected. In addition, the colorimetric sensing strategy was based on the efficient peroxidase-like activity of bCDs binding to Cu2+, catalyzing H2O2 to generate OH. Under this condition, TMB could be oxidized to form blue oxTMB. However, when glyphosate was involved in the system, the fluorescence of ZIF/CuNCs was restored upon due to the strong chelation between Cu2+ and glyphosate, while the peroxidase-like activity of bCDs/Cu2+ decreased and resulted in the generation of fewer oxTMB, accompanied by a lighter blue color. The sensing platform was successfully applied to the determination of glyphosate in real samples of lake water and cabbage, demonstrating reliable and sensitive performance in practical applications.

A smartphone-integrated portable platform based on polychromatic ratiometric fluorescent paper sensors for visual quantitative determination of norfloxacin

The emergence of “superbugs” due to antibiotics overuse poses a significant threat to human health and security. The development of sensitive and effective antibiotics detection is undoubtedly a prerequisite for addressing antibiotics overuse-associated issues. However, current techniques for monitoring antibiotics typically require costly equipment and well-trained professionals. Hence, we developed herein a rapid, instrument-free, and on-site detection method for antibiotic residues such as norfloxacin (NOR) based on a ratiometric sensing platform utilizing “on–off–on” response properties of polychromatic fluorescence for direct visual quantitative NOR analysis. Specifically, this platform integrated iron ions (Fe3+)-chelated blue carbon dots (BCDs) for signal sensing and red carbon dots (RCDs) as an internal reference. The sensor mechanism is selective quenching of BCDs' blue fluorescence by Fe3+ via an inner filter effect with unaffected RCDs' red fluorescence. Further NOR addition led to competitive binding with BCDs due to Fe3+ shedding from the BCDs’ surface for a recovered blue fluorescence signal. Notably, the ratiometric fluorescence sensor demonstrated rapid and highly sensitive NOR detection in a concentration range of 1–70 μM with an impressive detection limit of 6.84 nM. The ratiometric fluorescence sensing platform was constructed by integrating smartphone and paper-based strategies, which exhibited exceptional sensitivity, selectivity, and rapid response for portable, instrument-free, visual quantification of NOR in real samples.

Localized electron-accepted yellow-emission carbon dots encapsulated in UiO-66 for efficient visible-light driven photocatalytic activity

Metal organic frameworks (MOFs) possess a large surface area, inherent porosity and high crystallinity. Nevertheless, they lack electron acceptors, which limit the exploitation of their photocatalytic properties. Carbon dots (CDs) known for excellent optical properties can serve as localized electron acceptors. As a novel hybrid nanomaterial, the structure of CDs@MOFs effectively facilitates charge separation and carrier transfer, bring about a marked improvement of photocatalytic activity. In this study, yellow-emission carbon dots (YCDs) were encapsulated within zirconium-based metal organic framework (UiO-66) via a dynamic adsorption method. Compared with blue carbon dots (BCDs), the YCDs@UiO-66 exhibited superior degradation performance. It demonstrates that incorporation of YCDs broadens the UV absorption range of UiO-66, thereby enhancing light utilization. The degradation efficiency of YCDs@UiO-66 was 92.6%, whereas UiO-66 alone achieved only 63.1%. Notably, the results of the radical quenching experiment and electron paramagnetic resonance (EPR) revealed that h+ and •O2− played a prominent role in the photodegradation of tetracycline hydrochloride (TCH). This study highlights that the introducing YCDs in MOFs-mediated photocatalytic reactions is a viable strategy to improve catalytic efficiency.

One-pot synthesis of full-color carbon dots with N, O surface-state energy-gap-controlled emission

An easy and effective route for preparing full-color (blue, green, yellow and red) carbon dots (CDs) with brilliant and stable photoluminescent (PL) was developed by using gallic acid and o-Phenylenediamine as precursors. The resulting CDs were then separated by silica-gel column chromatography. The prepared four types of CDs owned high quantum yields (up to 11.2%) and exhibited attractive features such as excellent solubility, high stability, excitation wavelength-independent PL, mono-exponential PL lifetimes, low cell toxicity and homogeneous optical properties. Then, the mechanism of full-color CDs PL was explored. The results suggested that the surface-states of prepared CDs, especially the pyridine N (C = N) and C = O functional groups, were primarily responsible for the full-color PL emission. The blue CDs had the largest content of C = O while the CDs turned to be green as the C = O decreased and the C = N content increased. The surface state regulation of C = N bond was dominant in yellow CDs while red CDs possessed highest content of C = N and new –COOH appeared. The gradual substitution of C = N to C = O made the band gap of CDs narrowed, which is the main reason for the redshift of CDs PL emission peak. Importantly, the easy preparation and unique optical features of these CDs made them potentially useful in numerous applications such as full-color cell labeling, drug delivery and optoelectronic technologies.

Bright Blue Light‐Emitting Diodes Based on Well‐Modified Carbon Dots by Designing Co‐Host Systems to Balance Carriers’ Injection

AbstractLeveraging bright and stable carbon dots (CDs) for blue light‐emitting diodes (LEDs) is a prospective but challenging topic. Aggregation‐caused quenching (ACQ) of CDs and device engineering of CDs‐LEDs are two issues. Here, blue CDs with quantum yield of 59.75% are synthesized. Hydrogen bonds increase rigidity and facilitate luminescence, while polymer chains increase spatial resistance and resist ACQ. Then, solution‐processed blue CDs‐LEDs are assembled by blending CDs into poly(N‐vinylcarbazole) (PVK) as light‐emitting layer (EML). Furthermore, several other materials are also employed as the second host to reduce injection barrier, facilitate carriers’ transport, and balance carriers’ distribution. In particular, the blue CDs‐LED based on the co‐host system of PVK and 4‐[1‐[4‐[bis(4‐methylphenyl)amino]phenyl]cyclohexyl]‐N‐(3‐methylphenyl)‐N‐(4‐methylphenyl)benzenamine (TAPC) achieves a maximum brightness up to 827.60 cd m−2. This work is a step forward for applying CDs in LEDs.

Construction of dual-channel ratio sensing platform and molecular logic gate for visual detection of oxytetracycline based on biomass carbon dots prepared from cherry tomatoes stalk

In this work, blue carbon dots (Stalk-Trp CDs) with high fluorescence quantum yield were successfully prepared from biological waste cherry tomato stalk and tryptophan. The morphology, composition, and properties of Stalk-Trp CDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, infrared spectroscopy, ultraviolet–visible absorption spectroscopy, and fluorescence spectroscopy. On this basis, a dual-channel ratio sensing platform (Stalk-Trp CDs@Eu) was constructed using the interaction of Stalk-Trp CDs with Eu3+, which reduced the detection limit of the antibiotic oxytetracycline from 0.15 µmol/L to 0.018 µmol/L. Channel 1 of the dual-channel ratio sensing platform is a neutral environment (pH = 6.5), and the specific response of the probe to OTC causes its fluorescence to change from blue to purple. Channel 2 is an alkaline environment (pH = 11.5), and the fluorescence of the probe turns green only in the presence of OTC. The interaction mechanism of the dual-channel ratio sensing platform with the antibiotics oxytetracycline (OTC), chlortetracycline (CTC), and tetracycline (TC) was also revealed. The detection results of OTC in honey and milk by using Stalk-Trp CDs@Eu were highly consistent with the HPLC method recommended by the national standard. This shows that the dual-channel ratio sensing platform has great practical application value in the field of antibiotic detection.

Hydrogen-bond induced enhanced emission ratiometric fluorescent handy needle for visualization assay of amoxicillin by smartphone sensing platform.

Amoxicillin (AMO) is one of the most commonly used antibiotics, and its abuse in animal husbandry or clinical therapy can pose unpredictable hazards to humans. Therefore, it is crucial to develop a real-time and rapid method to accurately determine AMO content. Here, we designed a fluorescent nanoprobe for qualitative and quantitative AMO determination by using as-synthesized green safe materials of nontoxic red carbon dots (RCDs) and blue carbon dots (BCDs). In the presence of AMO, a reaction promoting hydrogen bonding occurred immediately, resulting in an instant increase in the intensity of the blue fluorescence of BCDs, accompanied by a marked color change from red to blue. For practical application, we designed a nontoxic sensing fluorescent handy needle to directly and quantitatively detect AMO in real samples. This portable and easy-to-use device was demonstrated on a smartphone platform based on 3D printing technology, which offers the advantages of simple production, excellent visualization, fast response, and instant quantitative detection. The device requires an extremely short detection time and has a sensitive detection limit of 2.39nM. The method presented here enables real-time assessment for food safety, as well as on-site detection under field conditions to track various trace substances for timely health checks.

Carbon dots with high quantum yields used for Fe3+ detection, information encryption and anti-counterfeiting

We prepared nitrogen doped blue carbon dots (B-CDs) and applied it in detection of Fe3+ and information encryption and anti-counterfeiting.

Facile Synthesis of Molecularly Imprinted Ratiometric Fluorescence Sensor for Ciguatoxin P-CTX-3C Detection in Fish

Ciguatoxin (CTX) detection methods are essential due to the serious hazard that bioaccumulation in fish and transmission along the food chain poses to human health. We report the rapid and simple development of a dual-emitting, molecularly imprinted, ratiometric fluorescence sensor (MIPs@BCDs/RCDs@SiO2) to detect ciguatoxin P-CTX-3C with high sensitivity and selectivity. The sensor was fabricated via sol–gel polymerization using monensin as the fragmentary dummy template molecule, blue carbon dots (BCDs) as the response signal, and red carbon dots (RCDs) as the reference signal. The fluorescence emission of BCDs was selectively quenched in the presence of P-CTX-3C, leading to a favorable linear correlation between the fluorescence intensity ratio (I440/I675) and the P-CTX-3C concentration in the range of 0.001–1 ng/mL with a lower detection limit of 3.3 × 10−4 ng/mL. According to LC-MS measurement results, the proposed sensor can rapidly detect ciguatoxin P-CTX-3C in coral reef fish samples with satisfactory recoveries and standard deviations. This study provides a promising strategy for rapid trace analysis of marine toxins and other macromolecular pollutants in complex matrices.

Carbon dot-decorated metal-organic framework composite for Fe3+ detection in the aqueous environment

The contamination of heavy metal ions in the aqueous environment constitutes an important threat to human survival. Hence, the development of simple, effective, and cheap detection of heavy metals and pesticide residues is essential for environmental control. Here, we synthesized a yellow carbon dots-linked ZIF-8 (yCDs/ZIF-8) composite, which was prepared with excellent photoluminescence properties and aqueous stability, and characterized by strong yellow fluorescence emission. The ratio metric fluorescence sensor has been constructed using its stable light blue carbon dots. The fluorescence sensor has excellent selectivity and sensitivity as a sensing probe for Fe3+ ions, with a detection limit of 0.3690 μM. In addition, the fluorescence quench mechanism was investigated. It has been shown that the yCDs/ZIF-8 fluorescence could be quenched by Fe3+ via static quenching and absorption competition mechanisms. The probe has high-quality application potential in terms of food safety and environmental monitoring due to the fact of its simplicity, high yield, and low cost.

Multicolor carbon dots assembled polyvinyl alcohol with enhanced emission for white light-emitting diode

Red carbon dots (R-CDs), yellow-green carbon dots (Y-CDs) and blue carbon dots (B-CDs) were successfully synthesized by one-step hydrothermal method using o-phenylenediamine and dopamine hydrochloride as raw materials by adjusting the pH of the reaction solvent. The Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS) spectra and optical properties of CDs show that these three CDs have similar types but different contents of functional groups, resulting in different fluorescence emission. R-CDs and Y-CDs compound with polyvinyl alcohol (PVA) to form bright R-CDs/PVA and Y-CDs/PVA phosphors, while B-CDs/PVA phosphors have weak fluorescence. Compared with R-CDs and Y-CDs solution, the fluorescence emission of the phosphors was significantly enhanced for the matrix inhibits the process of non-radiative transition. Based on the thermostability and broad emission peaks of CD-based phosphors, light-emitting diode (LED) was fabricated using R-CDs/PVA and Y-CDs/PVA phosphors as fluorescent material. The prepared LED exhibits white light with a color coordinate of (0.32, 0.33), correlated color temperature (CCT) of 6067 K and color rendering index (CRI) of 78.2. The environmental-friendly CD-based white light-emitting diode (WLED) was successfully fabricated.

Blue Carbon Dot-Based Portable Smartphone Platform for Visualization of Copper(II)

The acidic soil where tea grows makes the accumulation of copper ions (Cu2+) easy. Long-term drinking of tea infusions and tea beverages will cause abnormal accumulation of copper in the human body and endanger human health. Herein, we designed a visual portable smartphone platform based on ratiometric fluorescent nanoprobes for the rapid, real-time, and sensitive detection of Cu2+ in tea and tea beverages. We synthesized the ratiometric fluorescent nanoprobe formed by blue carbon dots (BCDs), which are used as internal standards, and a sensing reagent (diethyl-[5-(2-1,4,7,10-tetraaza-cyclododec-1-yl-acetylamino)-benzo[α]phenoxazin-9-ylidene]-ammonium (cyclen-NB)) for Cu2+. With an excitation wavelength of 330 nm, the emission wavelengths of cyclen-NB and BCDs are 674 and 451 nm, respectively. Cyclen-NB effectively captures Cu2+ to form a metal complex via a ligand-to-metal charge transfer (LMCT), resulting in obvious color changes from red to blue-violet. The designed ratiometric fluorescent nanoprobe has high sensitivity, good selectivity, and strong anti-interference ability, and the detection limit can be as low as 1.37 nM. Furthermore, a visual portable sensing platform was constructed based on the ratiometric fluorescent nanoprobe in combination with smartphones. The color recognition software of the smartphone can convert the color information of the photos taken by the mobile phone into digital data for analysis; and the detection limit is as low as 4.83 nM, and the yield rate is 86.79–111.20% (RSD ≤ 4.95). Therefore, the method reported in this manuscript can provide a convenient method for rapid on-site and visual inspection of tea and tea beverages for food safety.

A New Dual-peak Fluorescent Probe for Water Content Detection Made From Taxus.

In this paper, the leaves of Taxus were used as the sole carbon source, and two kinds of carbon dots blue and red, with different properties, were synthesized by the hydrothermal method under different conditions. The red carbon dots were quenched in the water, and the blue carbon dots had stable fluorescence properties in water environment. The bimodal fluorescence probe formed by mixing could accurately and stably measure the water content in ethanol, which was in the range of 82.5%-100%, is highly correlated with the fluorescence intensity ratio (I481/I678) of mixed carbon dots under 390nm excitation light, with R2 = 0.995 and the detection limit as low as 0.31%. The experimental materials are environmentally friendly, low in cost, and simple to operate, as well as the water content measured by proportional fluorescence has high accuracy, which provides a new method for measuring moisture in ethanol.

Quantitative Visual Detection of Mercury Ions With Ratiometric Fluorescent Test Paper Sensor.

A novel ratiometric fluorescence probe based on nitrogen-doped blue carbon dots (NCDs) and red gold nanoclusters (Au NCs) for mercuric ion (Hg2+) has been prepared and characterized. A user friendly fluorescent test paper based sensor combined with smartphone was fabricated for rapid visual and quantitative detection. Hg2+ can specifically bind to Au+ on the surface of Au NCs, leading to the quench of red fluorescence while the fluorescence intensity of the NCDs with blue fluorescence remained unchanged as a internal standard signal. The implement of paper-based sensor address some common drawback in analytical process such as the detection time, analysis cost. In a further demonstration, a homemade detection device with smartphone was used to qualify the Hg2+. After adding different concentration of Hg2+, red, purple, and blue colors were obtained on the detection zones of the fluorescent test paper. The Android App Color Grab was used to identify the red, green and blue (RGB) values of fluorescent color. The rapid visual and quantitative detection of Hg2+ was accomplished with the detection limit of 2.7 nM for fluorescence, 25 nM for smartphone and 32 nM for paper strip. The developed multi-mode detection platform was successfully applied to the detection of mercury ions in water samples with acceptable recoveries. The NCDs and Au NCs probe facilitate the one-site environmental monitoring for Hg2+ with “naked-eye” and smartphone.