RGB Analysis Research Articles

Highly sensitive and selective ratiometric fluorescence and colorimetric detection of Cr(VI) via in situ encapsulation of green/red carbon quantum dots in zeolite

To overcome the limitations arising from non-uniform particle size and solid-state aggregation of carbon quantum dots (CQDs), a novel dual-emissive ratiometric fluorescence probe, GCQDs@SBA-15/RCQDs@SBA-15 (G-RCQDs@SBA-15), has been successfully constructed by simplifying the synthesis process through in situ synthesis of CQDs in SBA-15 to further enhance their optical properties for highly sensitive detection of Cr(VI). The probe G-RCDs@SBA-15, based on green-emission carbon quantum dots (GCQDs) encapsulated in mesoporous molecular sieves SBA-15, provides the response signal, while red-emission carbon quantum dots (RCQDs) encapsulated in SBA-15 serve as an internal reference. The probe exhibits a satisfactory limit of detection (LOD) of 0.336 μM, which is 52 % lower than GCQDs/RCQDs. Importantly, the probe shows superior selectivity in detecting Cr(VI) compared to other metal ions. The fluorescence signal ratio of the probe decreases with increasing Cr(VI) concentration, resulting in a distinct change of fluorescence color from green to red. Based on UV–vis and fluorescence lifetime analysis, Inner filter effect (IFE) is considered the primary potential mechanism for the fluorescence color transition of G-RCDs@SBA-15 following the addition of Cr(VI). G-RCQDs@SBA-15 not only inherits the excellent optical properties of GCQDs and RCQDs but also shows high fluorescence and chemical stability. Considering the sensitive photoconversion properties of G-RCQDs@SBA-15, a smartphone-based laboratory device in combination with RGB analysis software has been used for Cr(VI) detection by directly capturing and analyzing fluorescence images. In addition, the sensing system is validated in the actual lake water samples, exhibiting recoveries from 83.3 % to 96.3 %, indicating its excellent practicality for Cr(VI) detection in real samples.

Dual-modal detection of antimicrobial susceptibility in pathogenic bacteria based on the high-throughput microfluidic platform

For pathogenic bacterial infectious diseases such as sepsis, accurate and rapid antimicrobial susceptibility testing (AST) plays an important role in improving antimicrobial screening and clinical outcomes. Traditional culture-based AST assays have the limitations of time-consuming, labor-intensive, expensive, and consuming reagents. In this work, a simple, fast, high-throughput microfluidic platform integrated with isolation, identification, and detection functions was designed for antibiotic susceptibility analysis in pathogenic bacteria. For the above purpose, MnO2@ZIF-90 nanoprobes with dual functions of nanozyme and fluorescence were prepared for visual eye or RGB analysis through a smartphone APP. More importantly, the redox activity of bacterial membrane in active pathogenic bacteria could decompose the MnO2 of MnO2@ZIF-90 nanoprobes and reduce the enzyme-like activity, which weakens the colorimetric signal of Timebox. Meanwhile, the ATP released from active pathogenic bacteria further triggered the breakdown of the inner ZIF-90 layer, generating a fluorescence signal. Therefore, a dual detection combining colorimetric and fluorescence was used to perform more accurate and reliable antibiotic susceptibility analysis of pathogenic bacteria. With the proposed microfluidic platform, a low detection of 10 CFU mL−1 bacteria and fast AST results were achieved within 5 min. The clinical applicability of the platform was further demonstrated through the analysis of clinical samples. This work provides a low-cost, easy-to-operation, fast-response, and high-throughput platform for the AST assays in pathogenic bacterial infectious diseases such as sepsis.

An Aggregation-Induced Emissive Platinum(II) Metallacycle as the Energy Donor of Rhodols for Ratiometric Detection of Hydrazine.

Industry-produced hydrazine (N2H4) is released into the environment, posing a major risk to human health and the ecosystem. Therefore, it is imperative to develop an effective and convenient method for the detection of N2H4. Herein, artificial light-harvesting systems (ALHSs) for N2H4 detection were constructed by applying an aggregation-induced emission-active platinum(II) metallacycle (TPEMc) as the energy donor and rhodols (P1, P2, and P3) as the energy acceptors. The ratiometric fluorescence probes based on ALHSs for N2H4 showed obvious signal amplification and lower limits of detection compared to those of rhodols (P1, P2, P3) alone. The TPEMc-rhodols systems clearly demonstrated a noticeable increase in fluorescence intensity at 550 nm and an obvious fluorescent color shift from cyan to yellow in the presence of N2H4. Fascinatingly, N2H4 could be visually and quantitatively detected in water by the TPEMc-rhodol systems paired with smartphone RGB analysis. Therefore, the combination of platinum(II) metallacycle with rhodols is a promising strategy for simple, sensitive, and visual detection of N2H4.

Real time monitoring of heavy metal adulteration in biodiesel using Arduino UNO platform@A promising multi-purpose stimuli-responsive azomethine based chemoreceptor for hierarchical tri-ionic sensing

The presence of metallic adulteration even in very trace level may lead to deleterious impact on the biodiesel quality and ultimately may be responsible for the dropping down of system efficiency, which necessitates the trace level recognition of heavy metal adulteration from biodiesel. In this context, herein using an azomethine functionalized chromogenic chemoreceptor, 1-((E)-(4-hydroxyphenylimino) methyl) napthalen-2-ol (HMN) has been reported for the selective chemodosimetric recognition of Cu2+ with a lower detection threshold of 7.8 ppb via distinct chromogenic variation of HMN. In addition to this, it has also exhibited selective and reversible naked eye chromogenic sensing behaviour towards F− (LOD=160 ppb) and Al3+ (LOD=48 ppb) at very trace level, which is quite lower than the WHO permissible limit. Distinct chromogenic recognition of F− by HMN proceeds via strong intermolecular hydrogen bonding mediated improved intramolecular charge transfer. The spectroscopic response of HMN in alternate presence and absence of the targeted analytes made it suitable to formulate AND-NOT-XNOR-NAND-OR gate based ‘Castle-like’ complicated logic circuitry. In-vitro cell imaging study using A549, human lung carcinoma cell line attests intracellular recognition capability of HMN, demonstrating its effectual bio-medicinal applications. Interestingly, inspired by the capability of HMN towards recognition of copper from biodiesel specimen, an RGB-assisted device comprised of TCS color sensor and an Arduino UNO 8-bit microcontroller has been developed for real-time quantitative analysis of the biodiesel adulteration. Going one step further, utilization of lab-on-a-box based prototype to monitor the concentration-dependent chromogenic fluctuation via RGB analysis is undoubtedly beneficial for the determination of copper adulteration in biodiesel sample. The presently developed chemoreceptor can thus be regarded as a valuable addition in the field of supramolecular chemistry as well as a significant initiative towards regular monitoring of the biodiesel quality control parameters as a part of sustainable environment.

Construction of a triple-mode sensing platform for effective differentiation, speciation, and monitoring of mercury and methylmercury bioaccumulation in crayfish via cation exchange reaction

Developing rapid and sensitive methods for monitoring inorganic mercury (Hg2+) and methylmercury (CH3Hg+) in crayfish is crucial for understanding the environmental impact of these contaminants. In this work, a novel tri-mode strategy was developed for highly sensitive monitoring of Hg2+ and CH3Hg+ bioaccumulation in crayfish by inductively coupled plasma mass spectrometry (ICP-MS)/ fluorescence /smartphone colorimetric (RGB) analysis without chromatographic separation. Cation exchange reaction (CER) was performed between Hg2+ and luminescent CdTe quantum dots (QDs), while CH3Hg+ unrealizable CER. The CH3Hg+ can be transformed to Hg2+ by simple UV irradiation, speciation analysis can be realized by detecting the fluorescence of CdTe QDs after incubation by Hg2+ and total Hg2+. In addition, the filtration of reacted CdTe QDs was carried out, ICP-MS was performed to detect exchanged Cd2+ by Hg2+ and total Hg2+, as well the smartphone RGB analysis was performed for membrane colorimetry. The limits of detection (LODs) of Hg2+ and CH3Hg+ for ICP-MS, fluorescence, and colorimetric (RGB) modes were 0.03 ng mL−1, 18 ng mL−1, and 0.9 μg mL−1 respectively. Density Functional Theory (DFT) was employed to validate the mechanism of the CER reaction. CdTe QDs array analysis with five different ligands was performed to eliminate potential ion interferences of Ag+ and Cu2+ that could occur during the CER reaction. The well-designed system was successfully utilized for monitoring trace Hg2+ and CH3Hg+ in crayfish fed Hg2+ and CH3Hg+ contaminative food over a two-week “uptake” period and a three-week “depuration” period. The results indicated that the Hg2+ uptake in different tissues was significantly different from that of CH3Hg+ in all tissues. There was evidence of Hg uptake from water via leaching from food, although the principal source of uptake was from food.

Ratiometric fluorescence sensor based on dye-encapsulated Zn-MOF for highly sensitive detection of diquat in tap water and apple samples

The development of convenient and intelligent visualization of rapid pesticide detection methods is key to ensuring food quality and safety. This paper presents a smartphone-based ratiometric fluorescence sensor for smart field visualization and detection of diquat (DQ). Three-dimensional Zn-MOFs are prepared by the solvothermal method using the rigid ligand 4,4′,4″-s-triazine-2,4,6-triyltribenzoic acid (H3TATB), the flexible ligand 1,4-bis((1H-imidazol-1-yl)methyl)benzene (bimb), and the transition metal (Zn2+), which shows good structural and thermal stability. Zn-MOF is a three-dimensional framework crystallizing in a triclinic crystal system in the Pī space group. Then, RhB@Zn-MOF is obtained by introducing rhodamine B (RhB) into the Zn-MOF framework using the same method. Internal Filter Effect (IFE) quenches red fluorescence and Fluorescence Resonance Energy Transfer (FRET) enhances blue fluorescence, enabling high sensitivity and visual detection of DQ. The sensor has a low detection limit of 10.50 nM and is linear over the 0–70.00 μM concentration range. Compared to Zn-MOF (detection limit of 16.90 nM), the introduction of RhB significantly improved the precision and sensitivity of DQ detection. The combination of a smartphone and RGB analysis enables fast and accurate quantitative analysis of DQ in tap water and apple samples. The sensor platform has the advantages of convenience, intelligent real-time detection, etc. It has a wide prospect of practical application and consolidates a solid foundation for food safety control.

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.

Handheld microfluidic multiple detection device for concurrent blood urea nitrogen and creatinine ratio determination using colorimetric approach

A novel microfluidic multiple detection (MMD) platform consisting of a microfluidic chip and a self-built detection system is proposed for determining the creatinine (CRE) and blood urea nitrogen (BUN) concentrations in whole blood samples. In the proposed approach, a drop of whole blood is injected into the inlet of the microfluidic chip and filtered through strips of hemofiltration paper. The plasma enters the BUN and CRE detection chambers and is absorbed by pre-placed test strips embedded with analyte-specific reagents. Secondary reagents are then introduced into the detection chambers using a finger pump, and the chip is heated to induce Berthelot and Jaffe reactions. An image of the reaction compounds is captured by a CMOS camera and transmitted to a smartphone, where the BUN and CRE concentrations are derived from predetermined calibration curves using RGB analysis software. The proposed MMD platform is demonstrated by comparing the results obtained for 43 whole blood samples collected from patients with chronic kidney disease (CKD) and health volunteers with the measurements obtained using a traditional benchtop system. The results confirm that the proposed MMD platform offers a cost-effective, convenient, and rapid technique for BUN/CRE ratio (BCR) determination in point-of-care (POC) contexts.

A novel fluorescence platform for portable and visual monitoring of meat freshness

Biogenic amines (BAs) are crucial markers of meat spoilage. Developing practical and effective BAs detection methods is essential for monitoring meat freshness and ensuring daily consumption safety. This study prepared several naphthalene-based fluorescent compounds to visually monitor meat freshness in real-time. These probes show a colorimetric fluorescence response to putrescine and cadaverine (typical spoilage indicators) through nucleophilic addition/elimination reaction. The detectability of these probes can be optimized by altering the electronegativity and substitution position of the recognition group. Among these compounds, 2-((6-(4-(diphenylamino)phenyl)naphthalen-2-yl)methylene)malono nitrile (TNMA) demonstrated exceptional sensing performance toward putrescine and cadaverine, including high-contrast fluorescence color transition (red to blue), rapid response times (∼30 s), high selectivity and sensitivity (detection limit for putrescine: 2.69 ppm, cadaverine: 6.11 ppm). Furthermore, the B/R values of TNMA test strips output by RGB analysis presented a linear correlation with total volatile basic nitrogen (TVBN, an international standard for evaluating food spoilage) values in pork. Based on this correlation, we utilized smartphone applications to construct an intelligent evaluation system, enabling visual monitoring of pork, chicken, and shrimp freshness under various storage conditions. The TNMA-based system offers a reliable platform for real-time, portable and visual monitoring of meat freshness for consumers and suppliers in the food industry.

A double responsive ratiometric and fluorimetric chemosensor based on dual-emitting thiophene-isoxazole derivatives and position effect of hydroxy group for monitoring gallium and copper ions using a smartphone

A series of simple Schiff bases, 2n-DHTC ((E)-N’-(2,n-dihydroxybenzylidene)-5-(thiophen-2-yl)isoxazole-3-carbohydrazide (n = 3,4,5,6)), with ICT characteristic were strategically constructed by rationally introducing 2,n-dihydroxybenzaldehyde (n = 3,4,5,6) into 5-(thiophen-2-yl)isoxazole-3-carbohydrazide and altering the position of another hydroxyl group. It was found that the position of the hydroxyl group on the dihydroxybenzaldehyde influence whether the sensor exhibited a colorimetric response, prompting further investigation into this phenomenon by DFT calculation. 25-DHTC, as a dual-emission fluorescent platform, demonstrated distinctive properties compared to other sensors, exhibiting ratiometric recognition towards Ga3+ ions and reversible fluorimetric quenching of Cu2+ ions in DMSO/H2O tris buffer. Meanwhile, limits of detection of 25-DHTC for Ga3+ and Cu2+ ions were as low as 15.0 nM and 2.4 nM, respectively. In addition, the 1:3 chelation stoichiometry between 25-DHTC and Ga3+/Cu2+ ions was confirmed, utilizing Job’s Plot analysis and mass spectrometric titration. The 25-DHTC sensor was employed to identify target ions in real water samples, while separate portable paper sensors were developed successfully for detecting Ga3+ ions. Subsequent visualization and assessment of real samples were performed through RGB analysis.

Construction of a sensor array using TiO2 NRs/CuO/rMIP with imprinted sites regulation as light-activated nanozyme to colorimetric detect fluoroquinolones

Fluoroquinolone antibiotics are widely used in daily life, but their abuse has caused serious problems, so it is very important to detect fluoroquinolones accurately and conveniently. In this study, a light-activated nanozyme sensor array (TiO2 NRs/CuO/rMIP) was prepared, and principal component analysis (PCA) was employed for qualitative and quantitative determination of four fluoroquinolones in water environments. The photoactive sites of TiO2 were determined by photo-deposition of CuO, and the molecularly imprinted sites was anchored to the photoactive site by the composite action between antibiotic templates and CuO, which led to the consistent adjustment of the imprinted sites and photoactive sites, thus enhancing the enzyme-like activity of TiO2 NRs/CuO/rMIP. In Addition, by adjusting the types and proportions of antibiotic templates during the preparation of MIP, TiO2 NRs/CuO/rMIP sensors with different response signals to four fluoroquinolones were prepared, and a sensor array was established based on them. Through an RGB analysis system of smart phone and PCA analysis method, qualitative and quantitative detection of the four fluoroquinolones was realized. The detection range of the four antibiotics was 0.1–3000 μM, which showed a good prospect for the actual detection of antibiotics.

Rapid redox-response featured visual ascorbic acid sensor based on simple-assembled europium metal-organic framework

A facile, fast and visible sensing platform for ascorbic acid (AA) detection has been developed based on self-assembled hydrangea-like europium metal-organic framework (HL-EuMOF). HL-EuMOF was synthesized through a simple one-step mixing process with Eu3+ and 1, 10-phenanthroline-2, 9-dicarboxylic acid at room temperature, which exhibited excellent properties including strong red fluorescence, long decay lifetime (548.623 μs) and good luminescent stability. Based on the specific redox reaction between Fe3+ and AA, the HL-EuMOF@Fe3+ was fabricated with “turn-off” response for AA, where the resulting Fe2+ displayed effective fluorescence quenching ability toward HL-EuMOF. The sensor demonstrated low detection limit (31.94 nM), rapid response time (30 s) and high selectivity. Integration of smartphone-assisted RGB analysis with HL-EuMOF@Fe3+ permitted convenient and visible quantitative determination of AA level. This approach also presented good detection performances in complex human serum and beverage samples, which could provide a valuable tool for AA detection in biomedical research and food industry.

Fluorescent and colorimetric dual-mode chemosensor for easy detection of Cu2+: Practical and smartphone-based application to test strip and water sample

A fluorescent and colorimetric dual-mode chemosensor HNHQ, based on the julolidine and naphthol moieties, was synthesized. Compound HNHQ exhibited unique photophysical properties of an intense fluorescence with a high quantum yield (Φ = 0.363) and a light yellow color through the ICT mechanism. HNHQ could detect Cu2+ through both a fluorescence turn-off and a colorimetry variation of light yellow to yellowish brown. HNHQ reacted with Cu2+ with a binding ratio of 1:1. The detection limit for Cu2+ was analyzed to be 1.60 μM for fluorescence and 1.32 μM for UV–vis, considerably below the safe value of 31.5 μM established by the World Health Organization (WHO). HNHQ analyzed Cu2+ in the pH range of 6–8 and reversibly identified Cu2+ by using ethylenediaminetetraacetic acid (EDTA). Moreover, HNHQ could effectively detect Cu2+ in mineral and tap water samples, in addition to test strips through fluorescent and colorimetric changes. As a portable probe, HNHQ was successfully applied to a smartphone-based RGB analysis for the quantitative examination of Cu2+. The detection mechanism of HNHQ for Cu2+ was illustrated by 1H NMR titration, ESI-MS analysis, and density functional theory (DFT) calculations.

Milk Spoilage Classification through Integration of RGB and Thermal Data Analysis

Milk Spoilage Classification through Integration of RGB and Thermal Data Analysis

Sulfato‐β‐cyclodextrin induced multivalent supramolecular directional aggregation of cyanovinylene derivatives for achieving reversible near‐infrared fluorescence

AbstractMolecular aggregation or supramolecular aggregation‐induced emission is one of the research hotspots in chemistry, biology, and materials. Herein, we report negatively charged sulfato‐β‐cyclodextrin (SCD) induced cyanovinylene derivatives (DPy‐6C) directional aggregation to form regular nanorods (DPy‐6C@SCD) through supramolecular multivalent interactions, not only achieves ultraviolet‐visible absorption redshifted from 453 to 521 nm but also displays near‐infrared (NIR) aggregation‐induced emission with a large spectral redshift of 135 nm. The DPy‐6C monomer presents random nanosheets with weak fluorescence but obtains regular aggregates after assembly with SCD through electrostatic interactions. In the presence of H+, the DPy‐6C@SCD can further aggregate into elliptical nanosheets without fluorescence changes due to the protonation of secondary amines. In contrast, the morphology of DPy‐6C@SCD becomes flexible and sticks together upon the addition of OH− with an emission blue shift of 72 nm and a 90‐fold intensity increase because of disrupting the stacking mode of aggregates, thereby achieving acid‐base regulated reversible fluorescence behaviors that cannot be realized by DPy‐6C monomer. The DPy‐6C@SCD can efficiently select the detection of volatile organic amines both in liquid and gas phases within 5 s at the nanomolar level. Taking advantage of RGB analysis and calculation formula application, the DPy‐6C@SCD has been successfully used to monitor various organic amines on a smartphone, accompanied by naked‐eye visible photoluminescence. Therefore, the present research provides an efficient directional aggregation method through supramolecular multivalent interactions, which not only realizes topological morphology transformation but also achieves reversible NIR luminescent molecular switch and high sensitivity organic amines fluorescent sensing devices.

An AIE and ESIPT based ratiometric fluorescent hydrogel sensor for detecting biogenic amines and chicken breast freshness

Meat quality is closely linked to food safety and human health, with freshness being a key indicator. Therefore, it is crucial to explore reliable and effective methods for detecting meat freshness. This study presented a ratiometric fluorescent hydrogel sensor based on aggregation-induced emission (AIE) and excited state intramolecular proton transfer (ESIPT) for this purpose. Tetraphenylene (TPE) and 2-(2′-hydroxyphenyl)-benzothiazole (HBT) fluorophore were intersected to generate TPE-HBT, and then a novel biogenic amines (BAs) detection ratiometric fluorescent probe, TPE-HBTAc, was successfully prepared by hydroxyl acetylation. TPE-HBTAc displayed a large Stokes shift and good photostability. It showed a significant response to the representative biogenic amine trimethylamine (TMA), with a ratiometric fluorescence change and low detection limit (LOD = 65 nM). Furthermore, BAs detection hydrogel sensor was created by mixing the fluorescent probe TPE-HBTAc in an agarose hydrogel with a 3D polymer network. The hydrogel sensor displayed a distinct color change from blue to yellow when exposed to TMA vapor under UV light and had a low detection limit (LOD = 5.88 ppm). The hydrogel sensor was utilized in conjunction with a smartphone RGB analysis system to determine the freshness of chicken breast samples. Consumers can easily observe the chicken breast freshness in real-time and non-destructively through UV flashlight illumination. The results of this work suggest that ratiometric fluorescent hydrogel sensor based on AIE and ESIPT can serve as a promising strategy to monitor food freshness.

Synthesis and characterization of a xanthene-based molecular probe to detect triphosgene in solution and vapor phases

The ability of a detection approach to direct a visible and easy-to-monitor characteristic is an important aspect of molecular-level detection. From this viewpoint, we developed the molecular probe Xanth-Py, which allows us to visually detect triphosgene (TPG) by modulating the probe's photophysical characteristics. Since Xanth-Py exhibits a strong fluorescence, its interaction with TPG causes the non-radiative decay of the probe. As TPG concentrations increase, the fluorescence intensity decreases linearly, leading to a nanomolar level detection limit. The interaction of Xanth-Py with TPG accompanied a color change from pink to blue, enabling a visible detection protocol. Probe-coated paper strips have been used as an inexpensive detection tool for vapor-phase TPG detection, revealing the potential of the Xanth-Py. Further, triphosgene has been detected using a smartphone-assisted RGB analysis tool in conjunction with a portable UV-light source device.

A smartphone-assisted portable sensing hydrogel modules based on UCNPs and Co3O4 NPs for fluorescence quantitation of hypoxanthine in aquatic products

Hypoxanthine is a promising index for evaluating the freshness of various aquatic products. Combined the hydrogels containing upconversion nanoparticles (UCNPs), Co3O4 NPs, and N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt/4-amino-antipyrine (TOPS/4-AAP) with a smartphone, a portable sensor was developed for the convenient, sensitive detection of hypoxanthine. With the H2O2 from xanthine oxidase (XOD)-catalyzed reactions of hypoxanthine, the fluorescence of UCNPs was effectively quenched by the purple product produced from the oxidization of TOPS/4-AAP catalyzed by Co3O4 NPs exhibiting peroxidase activity, among which the color change could be transformed into digital signals for quantification of hypoxanthine. The Green value in the RGB analysis of the fluorescence image was negatively proportional to hypoxanthine concentration in the range of 2.5–20 mg/L with a detection limit of 0.69 mg/L and a quantitation limit of 2.30 mg/L. Finally, this sensor was applied for hypoxanthine detection in real aquatic products, showing potential application for freshness evaluation of aquatic products.

Si,N co-doped carbon quantum dots in mesoporous molecular sieves: A fluorescence sensing platform for Cr(VI) detection

Carbon quantum dots (CQDs) are highly efficient fluorescent probes for metal ion detection; however, they are limited by non-uniform particle size, aggregation, and the inability to facilitate quantitative analysis. Herein, a smart host–guest strategy is utilized, wherein CQDs are immobilized in mesoporous molecular sieves, proving to be an effective method to minimize these drawbacks. Si,N-CQDs@SBA-15 is successfully synthesized by the one-step hydrothermal route using Si,N-CQDs precursor materials as guests and the mesoporous molecular sieve SBA-15 as the host. A good linear relationship between the concentration of Cr(VI) ions and fluorescent intensity is observed from 0 μM to 100 μM (R2 = 0.9986). Thelimitofdetection(LOD) is 0.213 μM, approximately three times lower than that of pristine Si,N-CQDs (0.677 μM). Additionally, Si,N-CQDs@SBA-15 exhibit good detection selectivity for Cr(VI) detection over other metal ions. Moreover, a smartphone-based laboratory device and RGB analysis app are employed to capture and analyze fluorescence images, revealing a LOD for Cr(VI) of 0.201 μM. Förster Resonance Energy Transfer (FRET) is identified as the possible mechanism for the fluorescence quenching of Si,N-CQDs@SBA-15 by Cr(VI) through UV–vis and fluorescence experiments. The practicability of the synthesized fluorescent probes is further validated in river water, yielding satisfactory spiked recoveries ranging from 99.24 % to 106.21 %.

Proposed prototype for a quantitative biosensor for insulin detection using a liquid crystal

In this paper, we present a novel approach for label-free detection of human insulin using 5CB liquid crystal (LC). Monitoring insulin levels in the body is essential for treating diseases like diabetes, which are caused by insufficient production or inefficient use of insulin. Contemporary techniques of detection rely on glucose detection, and limited information is available on the direct detection of insulin. A simple method using a common room temperature LC 4-cyano-4-pentyl biphenyl (5CB) interacting with different concentrations of insulin, observed through a polarising optical microscope (POM), is reported in this paper. An analysis of observed textures revealed the detection of insulin as low as 25 μM concentration. The distinguishable features of the observed textures provide a scale for estimating insulin concentration. The effect of different pH and salt concentrations was studied in order to understand the optimal working condition of the proposed biosensor. Image J analysis demonstrated a positive correlation (R2 equal to 0.9553) between grey index (GI) values and human insulin concentrations. RGB analysis and interference studies confirmed the biosensor’s specificity in insulin detection. To correlate the textures to the happenings at the molecular level, docking studies were carried out. In addition to this, properties such as aromaticity, H-bond, hydrophobicity, interpolated charges, ionizability and solvent accessible area (SAS) in the minimum energy binding sites of 5CB-LC and human insulin chains were measured to know more about the interaction properties. This novel strategy shows promise for improving insulin detection sensitivity and accuracy, ultimately leading to better diabetes management and healthcare outcomes.