Color Change Of Solution Research Articles

Rapid and practical colorimetric biosensor for leishmaniasis diseases

In this article, a colorimetric biosensor for detection of Leishmania major surface protease (Gp63) antibody (anti-gp63) was developed by using gold nanoparticle (AuNP) as a color reagent. The dispersion or aggregation of AuNPs leads to a distinct and sensitive change in UV-vis spectra and solution color. For this purpose, kinetoplastid membrane protein-11 (KMP-11) was labeled with AuNPs surface directly. After that, Gp63 antibody was added in the KMP-11@AuNP solution and a color change from red/pink to purple/violet was observed. As a result, anti-gp63 solution diluted at a ratio of 1:640 can be detected with the developed colorimetric leishmania biosensor. The relative standard deviation value for 1:320 diluted anti-gp63 was calculated as 1.29 %. Furthermore, the linear range of the developed colorimetric biosensor was determined as 1:80 to 1:640. Moreover, developed Leishmania biosensor was applied for detection of leishmania parasite crude antigen and rabbit serum which were used as positive and negative samples respectively. As a result, the recovery values for the measurements of aforementioned samples were calculated as 95.3 % ± 0.02, 103.1 % ± 0.02, 96.2 % ± 0.01 and 95.5 % ± 0.03 for dilutions of 1:200, 1:160, 1:320 and 1:640 anti-gp63 solutions respectively.

Cu/Co Bimetallic Carbon Catalyst as a Highly Efficient Promoter for Reactive Dyes Degradation with PMS.

The synergistic effect between bimetallic catalysts has been confirmed as an effective method for activating persulfate (PMS). Therefore, we immobilized copper-cobalt on chitosan to prepare bimetallic carbon catalysts for PMS activation and degradation of reactive dyes. Experimental results demonstrate that the CuCo-CTs/PMS catalytic degradation system exhibits excellent degradation performance toward various types of reactive dyes (e.g., Ethyl violet, Chlortalidone, and Di chlorotriazine), with degradation rates reaching 90% within 30 min. CuCo-CTs exhibit high catalytic activity over a wide pH range of 3-11 at room temperature and under static conditions, degrading over 92% of RV5 within 60 min. ultraviolet-visible (UV-vis) spectroscopy and color changes in the dye solution confirm the effective degradation of RV5, with a degradation rate of 97.2% within 10 min. Additionally, CuCo-CTs demonstrate good stability and reusability, maintaining a degradation rate of 92.8% after eight cycles. Kinetic studies indicate that the degradation follows pseudo-first-order kinetics. Furthermore, based on the results of radical scavenging experiments, the catalytic degradation mechanism of the dye involves both radical and nonradical pathways, with 1O2 identified as the primary active species. This study provides insights and experimental evidence for the application of persulfate oxidation in the treatment of dyeing wastewater.

A Naked-Eye Colorimetric Ratio Method for the Selective and Sensitive Detection of L-Cys Based on a Silver Nanoflakes–Chromium (III) Ion System

As a necessary sulfhydryl amino acid, L-cysteine (L-Cys) maintains many physiological functions in the biological system. However, abnormal L-Cys levels can cause a variety of diseases. In our work, a highly sensitive and selective assay has been developed for sensing L-Cys using the morphological transformation of silver-based materials induced by Cr3+. In this sensing system, Cr3+ could etch the silver nanoflakes into silver nanoparticles, accompanied by a change in absorbance, which decreases at 395 nm, creates a new peak at 538 nm, and keeps increasing the absorbance with the addition of Cr3+ concentration. Meanwhile, under the naked eye, the solution color changes from bright yellow to dark purple. Because of the strong affinity between L-Cys and Cr3+, L-Cys could inhibit the induction of Cr3+ on silver-based materials, thereby preventing changes in the configuration, absorption spectrum, and color of silver-based materials. Taking advantage of this point, we can quantitatively detect the concentration of L-Cys. A linear relationship between the absorbance ratio (A538 nm/A395 nm) and L-Cys concentration was found in the range of 0.1–0.9 μM, and the detection limit was 41.2 nM. The strategy was applied to measure L-Cys spiked in beer and urine samples, with recovery from 93.80 to 104.03% and 93.33% to 107.14% and RSD from 0.89 to 2.40% and 1.80% to 6.78%, respectively. This detection strategy demonstrates excellent selectivity and sensitivity, which makes it a practical and effective method for the detection of L-Cys in real samples.

Bimetallic CuFe Prussian Blue Analogue Nanocubes as a Colorimetric Probe for the Quantification of Glutathione

Label-free bimetallic CuFe Prussian blue analogue nanocubes (CuFe PBA NCs) were directly employed as colorimetric probes for the visual determination of glutathione (GSH). CuFe PBA NCs produce an absorption peak at 400 nm. In the presence of GSH, the CuFe PBA NCs were transformed into larger hollow nanospheres based on the acid-initiated Kirkendall effect, leading to the appearance of a new peak at 520 nm and a solution color change from yellow to red. Thus, the GSH-induced color changes allowed the establishment of a double-signal colorimetric assay for GSH using the ratio of absorbance at 520 and 400 nm (Δ(A520/A400)). Facile determination of GSH from 0.1 to 8 μM with satisfactory specificity was developed, providing a detection limit as low as 0.08 μM. Additionally, GSH concentrations exceeding 3 μM can be directly identified by the naked eye. The colorimetric assay for GSH has also been demonstrated to have application for serum analysis. Compared with conventional single-signal colorimetric determination, the ratiometric probe was demonstrated to provide good selectivity and high sensitivity.

Preparation, characterization, and application of pH-responsive biodegradable intelligent indicator film based on rose anthocyanins

An intelligent pH-responsive indicator film (CA/CMC/RA) was fabricated by blending carrageenan (CA), carboxymethylcellulose (CMC), and rose anthocyanin (RA). Fourier transform infrared spectroscopy revealed the formation of hydrogen bonds between CA/CMC and RA. X-ray diffraction analysis demonstrated that the addition of RA enhanced the crystallinity of CA/CMC films. The incorporation of RA altered the microstructure of CA/CMC composite films, resulting in a roughened surface. RA improved the a*, b*, thickness, opacity, and water vapor permeability of CA/CMC/RA films. Moreover, the addition of RA increased the elongation at break, while decreasing the tensile strength. RA significantly increased the antioxidant capacity of CA/CMC films. Furthermore, CA/CMC/RA films exhibited pH-responsiveness, showcasing distinct color changes in different buffer solutions. In the application test, the CA/CMC/RA indicator film was used as a label to monitor the freshness of the ribbon fish stored at 4 °C. The results indicated that the film's color changed from pink to yellow upon spoilage. The observations were consistent with the TVB-N value, which exceeded the set limit (30 mg/100g). Hence, the novel indicator film can serve as a food freshness indicator material.

Near-infrared photoelectrochemical and colorimetric dual-mode aptasensor for determining osteopontin based on Er-MOF nanoballs@gold nanoparticles and Au2Pt nanozymes

A near infrared photoelectrochemical (PEC) and colorimetric dual-mode aptasensor was fabricated for efficiently determining osteopontin (OPN). Er-MOFs and Au2Pt nanoparticles were successfully synthesized. The gold nanoparticles (AuNPs) modified Er-MOF (Er-MOFs@AuNPs) nanocomposites were introduced into the glassy carbon electrode (GCE) to construct a photoelectrochemical sensing interface. OPN aptamer (Apt1) was immobilized onto the Er-MOFs@AuNPs based photoelectrochemical platform through Au-S bond for the selectively recognizing osteopontin. Au2Pt-labeled OPN aptamer (Au2Pt-Apt2) was subsequently captured onto the OPN/Apt1/MOFs@AuNPs/GCE surface to form a sandwich sensing interface, leading to an enhancement on the photocurrent response. Interestingly, Au2Pt nanozyme which possesses peroxidase activity could produce a solution color change in the presence of 3,3′,5,5′-tetramethylbenzidine (TMB) and hydrogen peroxide. The variations of photocurrent response and absorbance can be employed for the quantitative detection of OPN. Under the optimal conditions, the PEC and colorimetric sensing strategies show linear responses towards OPN in the concentration range of 0.01 ∼ 25 ng mL−1 and 1 ∼ 850 ng mL−1, respectively. The calculated determination limits were 2.6 pg mL−1 and 0.04 ng mL−1. The PEC and colorimetric dual-mode sensing platform can provide no crosstalk results and can be mutually verified, thus effectively improving the accuracy and reliability for the determination of OPN.

Colorimetric Silver Ion Detection Based on Silver Metallization of Gold Nanorods

AbstractDespite the use of silver in various industries, this heavy metal can pose serious risks to living organisms and the environment. Therefore, the development of simple measurement strategies for detection of silver ions (Ag+) with high sensitivity is of great importance. In this research, gold nanorods (AuNRs) have been used as indicator element in colorimetric sensor, which provides the possibility of facile and visual detection of silver by forming gold@silver core‐shell nanostructures (Au@Ag NRs). The basis of this sensor is the metallization of silver on AuNRs through ascorbic acid (AA) as a reducing agent, which forms Au@Ag NRs. During this mechanism, Ag+ is converted to silver atom (Ago) in the presence of AA and the surface of AuNRs is coated by inducing metallization. Any changes in composition and dimensions of AuNRs will cause color changes in the detection solution and subsequently spectral changes. The obtained results showed a good correlation between silver concentration and probe response (λo–λ) in the range of 2.5 to 30.0 μmol L−1 with a detection limit of 1.3 μmol L−1. In addition, the evaluation of the sensor in water and soil samples showed that it has acceptable accuracy in detecting silver ions in real conditions.

Rapid visual dual-mode detection of Zr(IV) based on L-histidine functionalized gold nanoparticles.

Heavy metal pollution has always been a great threat to human health and safety. Compared with other heavy metals, although zirconium ion (Zr(IV)) is equally harmful, due to the lack of research on Zr(IV) in the biological systems and environment, its detection does not seem to have received the attention it deserves. Herein, a rapid visual dual-mode detection (colorimetric and chrominance method) of Zr(IV) based on L-histidine functionalized gold nanoparticles (HIS-AuNPs) has been reported. AuNPs and HIS-AuNPs before and after adding Zr(IV) were characterized by UV-Vis, TEM, DLS, Zeta potential, EDS and FT-IR, etc. These results showed that L-histidine was successfully modified on the surface of AuNPs by forming a stable Au-N bond, and its modification had little effect on the dispersion degree of AuNPs. After the addition of Zr(IV), interaction of this metal ion with the imidazolyl group on L-histidine can obviously cause the aggregation of HIS-AuNPs within 12min, and the dispersion state and particle size of HIS-AuNPs can be significantly changed. These two detection modes were established by means of absorbance and color change of solution, and being used in addition and recovery experiments of Zr(IV) in natural water. Under the optimal conditions, these two modes exhibited good linearity within 15-70 and 20-100μmolL-1, and limit of detection of 2.62 and 6.25μmolL-1. The proposed method was highly sensitive and selective, which provided a new convenient way to realize the detection of Zr(IV).

In-situ highly selective colorimetric trace level recognition of lead and copper ion in real samples by silver nanoparticles

In the current study, an advanced and highly discriminating scheme was developed to detect Pb+2 and Cu+2 using Maltol-capped silver nanoparticles (McAgNPs). Various metal ions i.e. Fe+3, Ce+4, Ni+2, Mg+2, Cd+2, Mo+6, Zn+2, Na+1, Co+2, Ba+2, Cu+2, and Pb+2 was studied, among them, only Pb+2 and Cu+2 caused substantial changes in solution color, shifting from yellow to green and pink immediately after adding AgNPs. This color transformation was accompanied by the emergence of new visible bands at 674 nm for Pb+2 and 608 nm for Cu+2. The characterization of complexes (McAgNPs-Pb+2 and McAgNPs-Cu+2) was carried out by state of art techniques such as visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR), and Atomic force microscopy (AFM). AFM results indicated an increase in particle size after the interaction (i.e., 40 to 150 (Cu+2) and 250 nm (Pb+2)). McAgNPs are remarkably selective for Pb+2 and Cu+2 in the presence of other metal ions (i.e., Fe+3, Ce+4, Mg+2, Ni+2, Mo+6, Zn+2, Cd+2, Co+2, Na+1, Ba+2). The pH effect on both complexes was also investigated over a range of pH 1.0–13.0, revealing that McAgNPs-Pb+2 remained stable across the entire pH range, while McAgNPs-Cu+2 was stable only under acidic conditions. Both interactions exhibited good linearity (0.4–1.0 μM), binding stoichiometry (1-Pb+2:1McAgNPs and 2-Cu+2:3McAgNPs), and their respective limit of detection (LOD) was found to be 0.035 for McAgNPs-Cu+2 and 0.067 μM for McAgNPs-Pb+2. Additionally, the suggested scheme was effectively utilized to detect Pb+2 and Cu+2 in environmental (e.g., lake, tap, mineral, and well water) and biological (e.g., urine and plasma) samples, with recoveries ranging from 94.7 to 105%. Consequently, our approach paves the way for creating innovative and efficient suitable nanoprobe for highly selective and sensitive sensing.

Preparation of Silver Nanoparticles Deposited on TEMPO-Oxidized Cellulose Nanofibers

Silver nanoparticles (AgNPs) were synthesized by a chemical method in which cellulose nanofibers (CNFs) extracted from pineapple leaves served as a stabilizing and reducing agent. In this study, pineapple leaves were oxidized by the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation with sodium hypochlorite (NaClO) to obtain CNFs. After the oxidation, the transformation from hydroxyl groups to carboxylate groups of cellulose was confirmed by Fourier-transform infrared spectroscopy (FTIR), and TEMPO-oxidized CNFs with a higher carboxylate content were obtained. Then, TEMPO-oxidized CNFs with a carboxylate content of 2.49 mmol/g and non-oxidized CNFs with a carboxylate content of 0.68 mmol/g were used as a reducing agent to synthesize AgNPs. The formation of AgNPs was confirmed by color changes of the Ag solutions from white to yellow. Furthermore, AgNPs with an average diameter of 76.5 ± 22.15 nm were obtained when TEMPO-oxidized CNFs were used as a reducing agent, while non-oxidized CNFs generated AgNPs with a larger particle size of 181.2 ± 66.16 nm. This suggested that the TEMPO-oxidized CNFs could be used as a stabilizing and reducing agent for the synthesis of AgNPs with smaller diameters.

Multipurpose arrowroot starch films with anthocyanin-rich grape pomace extract: Color migration for food simulants and monitoring the freshness of fish meat

Extraction of anthocyanins from grape pomace, is a way of valuing these abundant by-products with low added value. Its integration into films may allow it to be used in bioactive packaging, which creates new color and solubility properties for food and smart food packaging which tracks the freshness of fish. Films of arrowroot starch added with different concentrations of grape pomace extract (GPE) were flexible to handle, reddish and presented a high content of anthocyanins. The water vapor permeability increased by 17 %, while the tensile strength of arrowroot starch film decreased by 79 % with the addition of 40 % GPE. The addition of GPE increased the solubility of the starch film in aqueous and lipid food simulants by 121 and 119 %. The GPE pigment preferentially migrated to the aqueous simulant due to the hydrophilic nature of anthocyanins and starch. The GPE film showed distinguishable color changes in different pH buffer solutions from pink at pH 2 to light blue at pH 7 and slightly yellowish green at pH 10. When the composite films were monitored for fish meat freshness, the change in color of the film from reddish pink to slightly green after 96 h of storage at 25 °C was evident.

A naked-eye colorimetric assay for highly sensitive detection of CL-20 explosive

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) stands as the most energetically condensed explosive ever found, and poses a great security threat to humans. Here we report a naked-eye colorimetric assay for highly sensitive detection of CL-20. Through effective cascading of the hydrolysis process of CL-20 with nitrite-involved Griess reaction to yield a pink-colored azo product, the visual quantification of CL-20 is realized by taking advantage of corresponding colorimetric signals. Under optimal experimental conditions, the present colorimetric assay is successfully used for highly selective determination of CL-20 in deionized water and environmental water samples with a nanomolar sensitivity. The resulting limit of detection is much lower than conventional methods. Moreover, benefiting from the distinct color change of the detection solution, direct naked-eye semi-quantitative analysis of CL-20 is achieved with a threshold concentration of 1 μM. Such simple, cost-effective, selective, and highly sensitive visual colorimetric assay will have valuable applications in public safety, environmental monitoring, and other related fields.

A Chromogenic Probe for Detection of Biologically Important Anions and its Implications for Designing Molecular Logic Gates.

Detection of fluoride (F-), acetate (AcO-), and cyanide (CN-) anions is vital from the biological and environmental aspects. In the present contributions, we have introduced a simple Salen-type chromogenic sensor, BEN, to detect these biologically important anions. Changes in UV-visible absorption spectra and color of BEN solution from very pale yellow to pink color are similar for each of these anions and found to be reversible only in the case of F- ions in attendance of HSO4- ions. The estimated limit of detection of BEN solution for detecting F-, AcO-, and CN- anions is found to be below the micromolar (μM) concentration level. Our fabricated handy paper test kit is suitable for qualitatively naked-eye detection of the anions. An immediate quantitative estimation of these important anions is possible using our BEN employing a smartphone, avoiding any costly experimental setup.

Monitor the freshness of shrimp by smart halochromic films based on gelatin/pectin loaded with pistachio peel anthocyanin nanoemulsion

This paper focuses on the combination of gelatin (Gel), pectin (Pec), and Pistachio peel anthocyanins (PSAs) to develop a halochromic film for food applications (shrimp). The results of spectroscopic properties showed that the film components had proper interaction and compatibility. Furthermore, the addition of PSAs and Pec improved the thermal stability of films. The addition of Pec and PSAs significantly improved the physical properties and mechanical resistance of the films. So that, the permeability to water vapor and oxygen reduced from 2.81 to 2.74 (g‧s−1‧Pa−1‧m−1) and 5.25 to 4.70 (meq/kgO2), respectively. In addition, the strength and flexibility of halochromic film reached 0.7 MPa and 56 % compared to Gel film (0.62 MPa, and 46.96 %). Most importantly, the color changes of the smart film from cherry/pink to yellow/brown, which were proportional to the color changes of the anthocyanin solution at different pHs, were able to monitor the shrimp freshness and spoilage at room (20 °C) and refrigerated (4 °C) temperature for 14 days.

Rational synthesis of 1,3,4-thiadiazole based ESIPT-fluorescent probe for detection of Cu2+ and H2S in herbs, wine and fruits

Here, 1,3,4-thiadiazole unit was employed as novel excited state intramolecular proton transfer (ESIPT) structure to prepare favorable fluorescent probe. High selectivity and rapid response to Cu2+ was obtained and the settling reaction was also used to recover ESIPT characteristics of probe to achieve sequential detection of H2S. Remarkable color change of solution from colorless to bright yellow and fluorescence emission from green to dark realized the visual detection of Cu2+ by naked eyes and transition of probe into portable fluorescent test strips. As expected, L-E could be utilized to quantitatively sense Cu2+ and H2S in different actual water and food samples including herbs, wine and fruits. The limits of detection for Cu2+ and H2S were as low as 34.5 nM and 38.6 nM. Also, probe L-E achieved real-time, portable, on-site quantitative detection of Cu2+ via a colorimeter and a smartphone platform with limit of detection to 90.3 nM.

A Naphthoquinoline-Dione-Based Cu2+ Sensing Probe with Visible Color Change and Fluorescence Quenching in an Aqueous Organic Solution.

Copper metal ions (Cu2+) are widely used in various industries, and their salts are used as supplementary components in agriculture and medicine. As this metal ion is associated with various health issues, it is necessary to detect and monitor it in environmental and biological samples. In the present report, we synthesized a naphthoquinoline-dione-based probe 1 containing three ester groups to investigate its ability to detect metal ions in an aqueous solution. Among various metal ions, probe 1 showed a vivid color change from yellow to colorless in the presence of Cu2+, as observed by the naked eye. The ratiometric method using the absorbance ratio (A413/A476) resulted in a limit of detection (LOD) of 1 µM for Cu2+. In addition, the intense yellow-green fluorescence was quenched upon the addition of Cu2+, resulting in a calculated LOD of 5 nM. Thus, probe 1 has the potential for dual response toward Cu2+ detection through color change and fluorescence quenching. 1H-NMR investigation and density functional theory (DFT) calculations indicate 1:1 binding of the metal ion to the small cavity of the probe comprising four functional groups: the carbonyl group of the amide (O), the amino group (N), and two t-butyl ester groups (O). When adsorbed onto various solid surfaces, such as cotton, silica, and filter paper, the probe showed effective detection of Cu2+ via fluorescence quenching. Probe 1 was also useful for Cu2+ sensing in environmental samples (sea and drain water) and biological samples (live HeLa cells).

A dual-modal photothermal and smartphone colorimetric aptamer sensing platform for tobramycin assay

The gold nanoparticles (AuNPs) aggregation-induced colorimetric aptamer sensing platform is commonly employed in bioassays. However, it has certain limitations, such as the requirement of instruments like a spectrophotometer for accurate quantitative readout and the background color interference. In this work, a dual-mode photothermal (PT) and smartphone colorimetric aptamer sensing platform was developed for tobramycin (TOB) assay using a digital thermometer or smartphone. Single-standard DNA (ssDNA) was utilized to bind the surface of AuNPs and maintain the dispersion of AuNPs at high salt concentrations. After the addition of the TOB, aptamer will specifically bind with it and separate from the gold surface. Then the aggregation of AuNPs can be observed in salt conditions, accompanying the AuNPs solution color change (red–purple-blue) and enhancing the PT effect. The DNA structural influence was carefully investigated. Under optimum conditions, the TOB assay by PT and RGB colorimetric mode have the limits of detection (LODs) of 1.7 μM and 1.3 μM, respectively. Furthermore, it is well demonstrated by the determination of TOB in food samples, offering high selectivity and sensitivity. It has potential for future application in point-of-care testing (POCT) with the benefits of inexpensive, easy to operate, and high specificity.

Naked-eye rapid recognition of tyrosine enantiomers using silver triangular nanoplates as colorimetric probe

Recognizing and quantifying enantiomers of chiral molecule is of great importance in chemical, biological and pharmaceutical fields. Herein, we presented one simple-yet-efficient method of sensing tyrosine (Tyr) enantiomers. In this sensing, silver triangular nanoplates (AgTNPs) were used as colorimetric probes. L-Tyr quickly induced the color of AgTNPs solution to change from dark blue to light gray, whereas D-Tyr induced no change of the AgTNPs solution color. The obvious color change enables the naked eye to recognize Tyr enantiomer. The visual method was used to detect the enantiometric excess value of L-Tyr in the whole range (−100 % ∼ 100 %). This chiral sensing can be finished within 5 min using one simple ultraviolet–visible spectrometer or naked eye. Furthermore, the mechanism of this chiral sensing was explored. It was confirmed that this chiral sensing was based on AgTNPs’ intrinsic chirality. This chiral sensing is rapid, simple, and low-cost, and has great potential for chiral determination of Tyr.

Fluorescence-based ratiometric sensors as emerging tools for CN− detection: Chemical structures, sensing mechanisms and applications

Hazardous cyanide anions (CN−) are increasingly threatening the environment and human health due to their widespread use in industry and many other fields. Over the past three decades, a large number of probes have been reported to sensitively and selectively detect this toxic anion, while a rather limited number of ratiometric fluorescent probes have been developed. The ratiometric probes have significant potential in bio-imaging and biomedical applications because of the ability to detect CN− in a quick, convenient and affordable way. In this review, we introduce 42 ratiometric fluorescent probes reported in the past 6 years (2018–2023) for CN– detection. Our description includes the chemical structures, photo-physical properties, CN− sensing mechanisms, solution color changes, limits of detection (LODs) and/or various applications of these chemical probes. This review provides guidelines for design and development of a new ratiometric probe for effective CN− detection.

Silver nanoparticles (NPAg) using padina australis seaweed

The synthesis of silver nanoparticles (NPAg) using Padina australis seaweed as a bioreductor and AgNO₃ as a precursor through the green synthesis method was successfully achieved. This environmentally friendly approach utilized various concentrations of the seaweed extract and silver nitrate precursor, resulting in the formation of silver nanoparticles at each concentration variation. The stability of these nanoparticles was confirmed by the observable changes in solution color, maximum wavelength, absorbance, and peak length shift. The process exhibited consistent results, with minimal wavelength variation occurring within 1 to 6 hours, particularly at a concentration ratio of 3 mM and 5:10 mL extract to precursor. These findings demonstrate the potential of Padina australis seaweed in the sustainable production of silver nanoparticles, offering a green alternative for nanoparticle synthesis.