Visual detection of arginine, histidine and lysine using quercetin-functionalized gold nanoparticles

Colorimetric Sensor Based on the Oxidase-Mimic Supramolecular Catalyst for Selective and Sensitive Biomolecular Detection

We have engineered a colorimetric sensor capable of selective and sensitive detection of amino acids. This sensor employs a supramolecular copper-dependent oxidase mimic as the probe, stemming from our prior research. The oxidase mimic is constructed through the self-assembly of commercially available guanosine monophosphate (GMP), Fmoc-lysine, and Cu2+. It catalyzes the formation of a red product with a maximum absorbance at 510 nm. The changes in color and absorbance are responsive to both the concentrations and types of amino acids present. This effect is most pronounced in the presence of histidine, with a detection limit (LOD) of 6.4 nM. Furthermore, the catalytic probe can distinguish histidine from histamine and imidazole propionate, as well as 1-methyl-histidine from 3-methyl-histidine, based on their distinct coordination capacities with copper. This underscores the high selectivity of the sensing platform. Both theoretical simulations and experimental results (including UV-vis spectra, fluorescence, and EPR) indicate that the amino acids may engage in copper center coordination, thereby impeding O2 access to copper─a pivotal aspect of the oxidase catalysis. This sensing platform, characteristic of its swift response, simple fabrication, and exceptional sensitivity and selectivity, can also be applied to detect other biological analytes such as nucleotides. It holds potential for use in environmental and biochemical analyses.

PMMA/paper hybrid microfluidic chip for simultaneous determination of arginine and valine in human plasma

The simultaneous determination is reported of arginine (Arg) and valine (Val) amino acids in plasma using flower-shaped μPADs and PMMA/paper hybrid microfluidic chip based on AuNPs capped with R-thiazolidine-4-carboxylic acid (THP). In this article, the evaluation procedure is based on the smartphone colorimetric detection mechanism that results from the aggregation of the THP-AuNPs with the addition of amino acids and visual color change from red to blue. Arg and Val were selectively determined with good reproducibility and an acceptable linearity range. The flower-shaped (μPADs) provides many advantages, including low cost, reasonable sensitivity, simple and fast performance, simultaneous detection, disposable use, and high sample throughput compared with conventional colorimetric method using cuvette cells. The ratios between the absorbance wavelength at (A₆₅₀/A₅₂₅) and (A₆₈₅/A₅₂₅) are linearly proportional to the concentration of Arg and Val. Under the optimum conditions, the calibration range in aqueous solutions is 0.0068-100.0 and 0.0056-75.0 µM with a limit of detection of 2.25 and 1.86 nM for Arg and Val at pH 7.0, respectively. In the case of μPADs, the calibration curves for Arg and Val showed good linearity in the concentration range 0.01-75.0 µM. The detection limits for the analytes were 3.51 nM and 3.44 nM for Arg and Val, respectively. In addition, a PMMA/paper hybrid microfluidic chip was successfully employed to determine Arg and Val in plasma samples with a relative error below 5%.

Water-Soluble Single-Benzene Chromophores: Excited State Dynamics and Fluorescence Detection

Two water-soluble single-benzene-based chromophores, 2,5-di(azetidine-1-yl)-tereph- thalic acid (DAPA) and its disodium carboxylate (DAP-Na), were conveniently obtained. Both chromophores preserved moderate quantum yields in a wide range of polar and protonic solvents. Spectroscopic studies demonstrated that DAPA exhibited red luminescence as well as large Stokes shift (>200 nm) in aqueous solutions. Femtosecond transient absorption spectra illustrated quadrupolar DAPA usually involved the formation of an intramolecular charge transfer state. Its Frank−Condon state could be rapidly relaxed to a slight symmetry-breaking state upon light excitation following the solvent relaxation, then the slight charge separation may occur and the charge localization became partially asymmetrical in polar environments. Density functional theory (DFT) calculation results were supported well with the experimental measurements. Unique pH-dependent fluorescent properties endows the two chromophores with rapid, highly selective, and sensitive responses to the amino acids in aqueous media. In detail, DAPA served as a fluorescence turn-on probe with a detection limit (DL) of 0.50 μM for Arg and with that of 0.41 μM for Lys. In contrast, DAP-Na featured bright green luminescence and showed fluorescence turn-off responses to Asp and Glu with the DLs of 0.12 μM and 0.16 μM, respectively. Meanwhile, these two simple-structure probes exhibited strong anti-interference ability towards other natural amino acids and realized visual identification of specific analytes. The present work helps to understand the photophysic−structure relationship of these kinds of compounds and render their fluorescent detection applications.

A New Pyrroloquinoline-Derivative-Based Fluorescent Probe for the Selective Detection and Cell Imaging of Lysine

In this paper, a new pyrroloquinoline-derivative-based fluorescent probe, PQP-1, was prepared for the selective detection of Lys in living cells and natural mineral water for drinking. PQP-1 exhibited high selectivity, low limit of detection, and a wide pH range. PQP-1 could be successfully applied for imaging Lys in living cells and in natural mineral water for drinking. We expect that PQP-1 will expand the detection reaction mechanism and the practical biological applications of Lys.

Insights into Anti-Inflammatory Activity and Internalization Pathway of Onion Peel-Derived Gold Nano Bioconjugates in RAW 264.7 Macrophages

Green synthesis of nanoparticles plays an important role in their efficient therapeutic effects in various biomedical applications. Here, we prepared gold nano bioconjugates (GNBCs) from the ethyl acetate fraction of onion peels and investigated their anti-inflammatory activity in lipopolysaccharide-stimulated RAW 264.7 macrophages. The GNBCs were characterized by UV-visible spectroscopy, dynamic light scattering, and transmission electron microscopy. Comparative studies have been conducted among GNBCs, fractionate alone [onion peel drug (OPD)], and the standard drug dexamethasone in various anti-inflammatory assays. It was observed that GNBCs showed comparatively good therapeutic efficacy than the fractionate alone. At the lowest 10 μg/mL concentration, the GNBC and OPD exhibited 70.86 and 91.98% of reactive oxygen species production, 10.88 and 20.97 ng/μL of nitrite production, 337 and 378 pg/mL of TNF-α production, 27.1 and 30.64 pg/mL of IL-6 production, respectively, by maintaining a satisfactory cell viability. Moreover, to understand the mechanistic pathway of GNBCs in their entry into the macrophages, their localization, and duration, uptake studies have been performed where a caveolar-mediated endocytosis pathway is found to be prominent. Hence, this study will lead to the development of cheap, green synthesis of nano bioconjugates and their role in inflammation.

A novel modified chitosan/collagen coated-gold nanoparticles for 5-fluorouracil delivery: Synthesis, characterization, in vitro drug release studies, anti-inflammatory activity and in vitro cytotoxicity assay

We report herein the development of the novel nanohybrids of gold nanoparticles reduced/stabilized/coated with collagen (AuNPs@collagen) in the first layer and subsequently modified with biotin-quat188-chitosan (Bi-QCS) in the outer layer for 5-fluorouracil (5-FU) delivery to improve cellular uptake and promote specific cell targeting of the nanocarrier. The fabrication of the layer-by-layer technique on the surface of gold nanoparticles (AuNPs) can overcome the limitation of poor drug loading capacity of the classic AuNPs from 64.67% to 87.46%. The AuNPs@collagen coated by the Bi-QCS exhibits strong electrostatic interactions between drug anion (5-FU) and amine groups of the modified chitosan as well as hydrogen bonding. Furthermore, the Bi-QCS-AuNPs@collagen demonstrated a significantly higher anti-inflammatory activity in RAW264.7 macrophage cell line. The Bi-QCS-AuNPs@collagen enhanced the activity of 5-FU approximately 3.3-fold (HeLa) and 6.2-fold (A549), compared to the free 5-Fluorouracil. According to these results, it is very promising that Bi-QCS-AuNPs@collagen can be used as an effective drug delivery carrier in the future.

Pyranopyrazole based Schiff base for rapid colorimetric detection of arginine in aqueous and real samples

A novel pyranopyrazole-based Schiff base PPS has been synthesized via a condensation reaction between aldehyde and hydrazide derivatives of pyranopyrazole.

A hydrazone-based spectroscopic off-on probe for sensing of basic arginine and lysine

A simple probe BHN based on naphthol and benzothiazole is reported for detecting of arginine (Arg) and lysine (Lys) with high selectivity and sensitivity. The BHN in aqueous solution upon reacting with Arg or Lys induced a visible color change from colorless to yellow. The probe BHN can also be employed for fluorescence turn-on sensing of Arg and Lys with the limits of detection (LOD) of 5.20 × 10^-2 μM and 3.69 × 10^-2 μM, respectively. The naked eye colorimetric and fluorimetric detecting is lack of sensitive to other common amino acids including Gly, Ala, Ser, Pro, Val, Thr, Cys, Leu, Ile, Asn, Asp, Glu, Gln, Met, His, and Phe. The sensing mechanism has been proposed by pH investigation and ¹H NMR spectra.

Green Synthesis of Gold Nano-bioconjugates from Onion Peel Extract and Evaluation of Their Antioxidant, Anti-inflammatory, and Cytotoxic Studies

Plant secondary metabolites such as flavonoids demonstrate high degrees of antioxidant, anti-inflammatory, and anticancer activities. Among flavonoids, quercetin plays an important role in inflammation by downregulating the level of various cytokines. Thereby, in this work, onion (Allium cepa) peel was successfully utilized for the synthesis of gold nano-bioconjugates acting as a natural therapeutic drug. In this process, crude onion peel extract was first divided into different fractionates, namely, ethyl acetate, butanol, methanol, and water, and they were subjected to various preliminary studies of antioxidant activities. The ethyl acetate fractionate shows high antioxidant activities in all the assays. The bioactive components were identified and found to contain a high amount of quercetin as confirmed by liquid chromatography with tandem mass spectrometry and high-performance liquid chromatogrpahy. Three gold nano-bioconjugates were prepared with different concentrations of the ethyl acetate fractionate. Various biochemical anti-inflammatory assays were carried out and compared with the active ethyl acetate fraction of the onion peel drug (OPD). The cytotoxicity of the nano-bioconjugate system and the OPD was checked in the myoblast L6 cell line from skeletal muscle tissues to evaluate the toxicity. All the three nano-bioconjugates A, B, and E demonstrated high percentages of cell viability, viz., 73.07, 72.3, and 69.15%, respectively, at their highest concentration of 200 μg/mL. The OPD also showed 88.56% cell viability with no toxic effects in the myoblast L6 cell line from skeletal muscle tissues. The reactive oxygen species reduction of nano-bioconjugate B showed a marked reduction of 76.77% at a maximum concentration of 200 μg/mL, whereas the OPD showed 68.17%. Hence, through this work, a cheap source of nano-bioconjugates is developed, which can act as a potent antioxidant and anti-inflammatory agent and are more active in comparison to the OPD alone.

Recent Advances in Sensing Applications of Molecularly Imprinted Photonic Crystals

Photonic crystals (PhCs) with a brightly colored structure are novel materials and are widely used in chemical and biological sensing. Combining PhCs with molecular imprinting technology (MIT), the molecularly imprinted PhC (MIPC) sensors are fabricated, which can specifically recognize the target molecules. Aside from high sensitivity and selectivity, the MIPC sensors could recognize the naked eye detection because of its optical properties. In this review, an overview of recent advances in sensing applications of MIPC sensors including the responsive mechanisms, application in environmental monitoring, and the application to human health were illustrated. The MIPC sensors all responded to the analytes specifically and also showed high sensitivity in real samples, which provided a method to realize the rapid, convenient, naked eye, and real-time detection. Furthermore, the current limitations and potential future directions of MIPC sensors were also discussed.

A simple and cost-effective paper-based and colorimetric dual-mode detection of arsenic(iii) and lead(ii) based on glucose-functionalized gold nanoparticles

We report a simple and cost-effective paper-based and colorimetric dual-mode detection of As(iii) and Pb(ii) based on glucose-functionalized gold nanoparticles under optimized conditions. The paper-based detection of As(iii) and Pb(ii) is based on the change in the signal intensity of AuNPs/Glu fabricated on a paper substrate after the deposition of the analyte using a smartphone, followed by processing with the ImageJ software. The colorimetric method is based on the change in the color and the red shift of the localized surface plasmon resonance (LSPR) absorption band of AuNPs/Glu in the region of 200-800 nm. The red shift (Δλ) of the LSPR band observed was from 525 nm to 660 nm for As(iii) and from 525 nm to 670 nm for Pb(ii). The mechanism of dual-mode detection is due to the non-covalent interactions of As(iii) and Pb(ii) ions with glucose molecule present on the surface AuNPs, resulting in the aggregation of novel metal nanoparticles. The calibration curve gave a good linearity range of 20-500 μg L-1 and 20-1000 μg L-1 for the determination of As(iii) and Pb(ii) with the limit of detection of 5.6 μg L-1 and 7.7 μg L-1 for both metal ions, respectively. The possible effects of different metal ions and anions were also investigated but did not cause any significant interference. The employment of AuNPs/Glu is successfully demonstrated for the determination of As(iii) and Pb(ii) using paper-based and colorimetric sensors in environmental water samples.

Optimally biosynthesized, PEGylated gold nanoparticles functionalized with quercetin and camptothecin enhance potential anti-inflammatory, anti-cancer and anti-angiogenic activities

BACKGROUND

The development of nano delivery systems is rapidly emerging area of nanotechnology applications where nanomaterials (NMs) are employed to deliver therapeutic agents to specific site in a controlled manner. To accomplish this, green synthesis of NMs is widely explored as an eco-friendly method for the development of smart drug delivery system. In the recent times, use of green synthesized NMs, especially metallic NMs have fascinated the scientific community as they are excellent carriers for drugs. This work demonstrates optimized green, biogenic synthesis of gold nanoparticles (AuNPs) for functionalization with quercetin (QT) and camptothecin (CPT) to enhance potential anti-inflammatory, anti-cancer and anti-angiogenic activities of these drugs.

RESULTS

Gold nanoparticles were optimally synthesized in 8 min of reaction at 90 °C, pH 6, using 4 mM of HAuCl4 and 4:1 ratio of extract: HAuCl4. Among different capping agents tested, capping of AuNPs with polyethylene glycol 9000 (PG9) was found best suited prior to functionalization. PG9 capped AuNPs were optimally functionalized with QT in 1 h reaction at 70 °C, pH 7, using 1200 ppm of QT and 1:4 ratio of AuNPs-PG9:QT whereas, CPT was best functionalized at RT in 1 h, pH 12, AuNPs-PG9:CPT ratio of 1:1, and 0.5 mM of CPT. QT functionalized AuNPs showed good anti-cancer activity (IC50 687.44 µg/mL) against MCF-7 cell line whereas test of anti-inflammatory activity also showed excellent activity (IC50 287.177 mg/L). The CAM based assessment of anti-angiogenic activity of CPT functionalized AuNPs demonstrated the inhibition of blood vessel branching confirming the anti-angiogenic effect.

CONCLUSIONS

Thus, present study demonstrates that optimally synthesized biogenic AuNPs are best suited for the functionalization with drugs such as QT and CPT. The functionalization of these drugs with biogenic AuNPs enhances the potential anti-inflammatory, anti-cancer and anti-angiogenic activities of these drugs, therefore can be used in biomedical application.

Solvothermal preparation of luminescent zinc(II) and cadmium(II) coordination complexes based on the new bi-functional building block and photo-luminescent sensing for Cu2+, Al3+ and L-lysine

In industry, over usage of Cu²⁺ and Al³⁺ will lead to toxic wastewater, which further to give serious pollution for the environment. On the other hand, L-lysine can enhance serotonin release in the amygdala, with subsequent changes in psychobehavioral responses to stress. Therefore it is the urgent problem to design a method for detecting the amount of Cu²⁺, Al³⁺, and L-lysine. In this work, through the solvothermal synthesis method, two new coordination complexes based on the new bifunctional building block 4'-(1H-1,2,4-triazole-1-yl)- [1,1'-biphenyl]-4-carboxylic acid (HL) have been synthesized, namely, [Zn(L)₂·4H₂O] (complex 1) and [Cd(L)₂·4H₂O] (complex 2). X-ray single-crystal diffractometer was used to analyze its structure, powder X-ray diffraction (PXRD) patterns confirmed that 1 and 2 powder's purity and 1 can keep stable during the detection process of Cu²⁺, Al³⁺, and L-lysine, respectively. Elemental analysis, thermogravimetric analysis, infrared analysis, ultraviolet analysis and fluorescent spectrum have been used to characterize these complexes. The photo-luminescent test showed that 1 can accurately recognize Al³⁺ and Cu²⁺ among various cations. On the other hand, 1 can distinguish L-lysine among amino acid molecules. Therefore, 1 can be utilized as a multifunctional fluorescent probe for Al³⁺(K_sv = 1.5570 × 10⁴ [M]^-1), Cu²⁺(K_sv = 1.4948 × 10⁴ [M]^-1) and L-lysine (K_sv = 4.9118 × 10⁴ [M]^-1) with low detection limits (17.5 μM, 18.2 μM, 5.6 μM) respectively.

Colorimetric detection of Cr3+ in dietary supplements using a smartphone based on EDTA and tannic acid-modified silver nanoparticles

A simplistic, portable and low-cost method for the rapid detection of Cr³⁺ was developed based on a smartphone readout and a co-functionalized silver nanoparticles (AgNPs) system for use as an on-site device in resource-poor areas. The presence of Cr³⁺ induced aggregation of AgNPs through coordinated complex formation between Cr³⁺ and stabilizing agents on the NPs surface, resulted in a bright yellow of an AgNPs solution turned to wine red along with a SPR band was red-shifted from 429 nm to 625 nm. A smartphone with an available free application, called "PhotoMetrix" was used to measure the RGB (red, green, blue) values of the color intensities in the AgNPs system and convert into Cr³⁺ concentration by using univariate calibration curves in less than 60s. This smartphone-based detection system showed a high selectivity of AgNPs with Cr³⁺ and gave a positive coefficient correlation (R² = 0.9878) between the intensity of channel R and the Cr³⁺ concentration, with a linear range of 2.0-5.0 mg L^-1, and a detection limit of 1.52 mg L^-1. Furthermore, the proposed method has been successfully applied for quantification of Cr³⁺ in dietary supplement samples. The results obtained were in close agreement with those obtained in FAAS (Flame Atomic Absorption Spectrometry). The developed colorimetric system based on a smartphone readout device exhibits feasibility and reliability for on-site Cr³⁺ detection in the real samples.

A paper-based colorimetric sensor array for discrimination and simultaneous determination of organophosphate and carbamate pesticides in tap water, apple juice, and rice

A colorimetric paper-based sensor is proposed for the rapid monitoring of six major organophosphate and carbamate pesticides. The assay was constructed by dropping gold and silver nanoparticles on the hydrophilic zones of a paper substrate. The nanoparticles were modified by L-arginine, quercetin, and polyglutamic acid. The mechanism of sensing is based on the interaction between the pesticide and the nanoparticles. The color of nanoparticles changed during the interactions. A digital camera recorded these changes. The assay provided a unique response for each studied pesticide. This method can determine six individual pesticides including carbaryl, paraoxon, parathion, malathion, diazinon, and chlorpyrifos. The limit of detection for these pesticides were 29.0, 22.0, 32.0, 17.0, 45.0, and 36.0 ng mL^-1, respectively. The assay was applied to simultaneously determine the six studied pesticides in a mixture using the partial least square method (PLS). The root mean square errors of prediction were 11, 8.7, 9.2, 10, 12, and 11 for carbaryl, paraoxon, parathion, malathion, diazinon, and chlorpyrifos, respectively. The paper-based device can differentiate two types of studied pesticide (organophosphate and carbamate) as well as two types of organophosphate structures (oxon and thion). Furthermore, this sensor showed high selectivity to the pesticides in the presence of other potential species (e.g., metal ions, anions, amino acids, sugar, and vitamins). This assay is capable of determining the pesticide compounds in tap water, apple juice, and rice samples.Graphical abstract.

A fluorescein-gold nanoparticles probe based on inner filter effect and aggregation for sensing of biothiols

Cysteine (Cys), homocysteine (HCys) and glutathione (GSH) are sulfhydryl-containing amino acids known as biothiols being able to bind to gold nanoparticles (AuNPs) via sulfhydryl group, resulting in the aggregation of AuNPs. Owning to their inner filter effect, AuNPs can weaken or even quench the fluorescence of fluorescein. However, the introduction of biothiols to fluorescein-AuNPs leads to the recovery of fluorescein fluorescence. Thus, a simple and reliable turn on fluorescence method was developed for monitoring biothiols with fluorescein-AuNPs as a probe. Several factors, including AuNPs concentration, pH value and incubation time, which might influence the fluorescence reclamation of fluorescein-AuNPs probe, were optimized by taking Cys as an example at room temperature. Under the optimal conditions, sensitive sensing of Cys, HCys and GSH was achieved. The detection limits for Cys, GSH, and HCys were 0.027, 0.023, and 0.030μΜ, respectively. This method was used to the determination of Cys in human serum samples with high precision and accuracy, indicating the potential of the method in practical applications with simple operation, good accuracy and high sensitivity.

Quinoline appended pillar[5]arene (QPA) as Fe3+ sensor and complex of Fe3+ (FeQPA) as a selective sensor for F-, arginine and lysine in the aqueous medium

A quinoline functionalized pillar[5]arene, QPA has been prepared and its interaction with biologically relevant ions and molecules in aqueous solution has been demonstrated. The sensor molecule, QPA has shown selectivity towards Fe³⁺ among eleven metal ions studied. The Fe³⁺ complex of QPA (FeQPA) selectively interacts with F^- among halides by ∼4 fold fluorescence enhancement. Further, FeQPA has shown selectivity towards arginine and lysine among twenty naturally occurring amino acids. The binding of QPA with Fe³⁺ has been confirmed by MALDI-TOF and ¹H NMR titrations.

Electrosynthesis of carbon aerogel-modified AuNPs@quercetin via an environmentally benign method for hydrazine (HZ) and hydroxylamine (HA) detection

An ultrasensitive electrochemical sensor fabricated using a hydrothermal and environmentally benign methods for the detection of environmental pollutions, namely, hydrazine (HZ) and hydroxylamine (HA) has been described.

Ultrasonic preparation of near-infrared emission cluster-based YbIII and NdIII coordination materials: Ratiometric temperature sensing, selective antibiotics detection and "turn-on" discrimination of l-arginine

Currently near-infrared (NIR) luminescence of lanthanide ions has received great attention because of their unique emissions in the near-infrared region (800-1700 nm). These NIR luminescent materials behave excellent applications in many fields such as sensors and probes in optical amplification, laser systems, biological systems and organic light-emitting diodes. In this work, two new near-infrared (NIR) emission three-dimensional (3D) Yb^III and Nd^III cluster-based coordination materials, namely {[Yb₂(L)₂(DMF)(H₂O)₄]·(DMF)₂ (H₂O)}_n (NIR-MOF 1) and [Nd(L)(DMF)₂]_n (NIR-MOF 2) (H₃L = terphenyl-3,4″,5-tricarboxylic acid) have been synthesized through the facile sono-chemical preparation methods. Both the near-infrared materials 1 and 2 have been characterized by single crystal X-ray diffraction, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Further the mixed-lanthanide near-infrared emission material Nd_0.35Yb_0.65L (NIR-MOF 3) can also be prepared under the sono-chemical conditions. NIR-MOF 3 can be successfully applied as the ratiometric NIR-MOF-based thermometer, which should origin from the emission intensity ratio between Yb³⁺ (976 nm) and Nd³⁺ (1056 nm) in the temperature range of 308-348 K. Besides these, the micro-morphologies of NIR-MOF 1 can be deliberately tuned through different sono-chemical reaction factors (reaction time, reaction temperature and sono-chemical powers). These tuned nano-sized materials NIR-MOF 1 (100 W, 80 min) can be utilized as the fluorescent sensing material to distinguish furazolidone and sulfasalazine from other antibiotics. At the same time, NIR-MOF 2 can be applied as the first example of MOFs-based sensors for discriminating l-arginine from other amino acids through the "turn-on" mode in the near-infrared emission region.

Application of functionalized silver nanoparticles as a biochemical sensor for selective detection of lysozyme protein in milk sample

Silver nanoparticles (AgNPs) functionalized with glutamic acid (GA) was used as a biochemical sensing probe in colorimetry for detection of lysozyme protein in milk samples. The method is based on the color change of AgNPs/GA from yellow to reddish-yellow differentiated with naked eyes for qualitative determination and red shift of localized surface plasmon resonance (LSPR) absorption signal intensity of AgNPs/GA in visible region used for quantitative determination of lysozyme. The control experiments were performed to demonstrate the electrostatic force of interactions between AgNPs/GA and protein molecule. A wide linear range of 3-150 nM with limit of detection of 1.5 nM was acquired for quantitative determination of lysozyme using AgNPs/GA as a biochemical sensing probe. The advantages of using AgNPs/GA as a biochemical sensing probe are simple, label-free and economic for determination of lysozyme from milk samples.

A colorimetric and ratiometric fluorescent sensor for sequentially detecting Cu2+ and arginine based on a coumarin–rhodamine B derivative and its application for bioimaging

In this work, a colorimetric and ratiometric fluorescent sensor based on a coumarin–rhodamine B hybrid for the sequential recognition of Cu²⁺ and arginine (Arg) via the FRET mechanism was designed and synthesized. With the addition of Cu²⁺, the solution displayed a colorimetric change from pale yellow to pink which is discernible by the naked eye. Additionally, the fluorescence intensities of the sensor exhibited ratiometric changes for the detection of Cu²⁺ at 490 and 615 nm under a single excitation wavelength of 350 nm, which corresponded to the emissions of coumarin and rhodamine B moieties, respectively. The fluorescence color change could be visualized from blue to pink. The limits of detection were determined to be as low as 0.50 and 0.47 μM for UV-vis and fluorescence measurements, respectively. More importantly, the sensor not only can recognize Cu²⁺ and form a sensor-Cu²⁺ complex but can also sequentially detect Arg with the resulting complex. The detection limits for Arg were as low as 0.60 μM (UV-vis measurement) and 0.33 μM (fluorescence measurement), respectively. A fluorescence imaging experiment in living cells demonstrated that the fabricated sensor could be utilized in ratiometric fluorescence imaging towards intracellular Cu²⁺, which is promising for the detection of low-level Cu²⁺ and Arg with potentially practical significance.

A FRET-based colorimetric and ratiometric coumarin–rhodamine B fluorescent sensor was designed, and its sensing behaviors for sequentially detecting Cu²⁺ and arginine were studied systematically.

Independent spectral characteristics of functionalized silver nanoparticles for colorimetric assay of arginine and spermine in biofluids

A colorimetric assay for selective and sensitive detection of arginine and spermine using 6-ATT-AgNPs as a probe.

Highly selective and sensitive determination of dopamine in biological samples via tuning the particle size of label-free gold nanoparticles

Herein, a rapid, sensitive and selective approach for the colorimetric detection of dopamine (DA) was developed utilizing unmodified gold nanoparticles (AuNPs). This assay relied upon the size-dependent aggregation behavior of DA and three other structurally similar catecholamines (CAs), offering highly specific and accurate detection of DA. By means of this study, we attempted to overcome the tedious procedures of surface premodifications and achieve selectivity through tuning the particle size of AuNPs. DA could induce the aggregation of the AuNPs via hydrogen-bonding interactions, resulting in a color change from pink to blue which can be monitored by spectrophotometry or even the naked-eye. The proposed colorimetric probe works over the 0.1 to 4μM DA concentration range, with a lower detection limit (LOD) of 22nM, which is much lower than the therapeutic lowest abnormal concentrations of DA in urine (0.57μM) and blood (16μM) samples. Furthermore, the selectivity and potential applicability of the developed method in spiked actual biological (human plasma and urine) specimens were investigated, suggesting that the present assay could satisfy the requirements for clinical diagnostics and biosensors.

Dually emitting gold-silver nanoclusters as viable ratiometric fluorescent probes for cysteine and arginine

Glutathione coated gold and silver nanoclusters (GSH-Au/AgNCs) were synthesized by one-pot reduction methods and are found to be viable fluorescent nanoprobes for cysteine (Cys) and arginine (Arg), with good selectivity over other amino acids. The GSH-Au/AgNCs have two emissions at 616 nm and 412 nm when excited at 360 nm. With the increased concentration of Cys, the ratio of the emission intensities (I₆₁₆/I₄₁₂) linearly decreases with Cys in concentration ranging from 0.05 to 10 μM and from 10 to 50 μM, respectively. With increased concentrations of Arg, the ratio of I₆₁₆/I₄₁₂ linearly decreases with Arg concentration ranging from 0 to 50 μM and from 50 to 100 μM, respectively. The probe was applied to the determination of Cys and Arg in spiked samples of serum and urine where it gave good recoveries. Graphical abstract Glutathione-coated gold and silver nanoclusters (GSH-Au/AgNCs) were synthesized by one-pot reduction and are found to be viable fluorescent nanoprobes for cysteine (Cys) and arginine (Arg).

A molecular rotor based ratiometric sensor for basic amino acids

The inevitable importance of basic amino acids, arginine and lysine, in human health and metabolism demands construction of efficient sensor systems for them. However, there are only limited reports on the 'ratiometric' detection of basic amino acids which is further restricted by the use of chemically complex sensor molecules, which impedes their prospect for practical applications. Herein, we report a ratiometric sensor system build on simple mechanism of disassociation of novel emissive Thioflavin-T H-aggregates from heparin surface, when subjected to interaction with basic amino acids. The strong and selective electrostatic and hydrogen bonding interaction of basic amino acids with heparin leads to large alteration in photophysical attributes of heparin bound Thioflavin-T, which forms a highly sensitive sensor platform for detection of basic amino acids in aqueous solution. These selective interactions between basic amino acids and heparin allow our sensor system to discriminate arginine and lysine from other amino acids. This unique mechanism of dissociation of Thioflavin-T aggregates from heparin surface provides ratiometric response on both fluorimetric and colorimetric outputs for detection of arginine and lysine, and thus it holds a significant advantage over other developed sensor systems which are restricted to single wavelength detection. Apart from the sensitivity and selectivity, our system also provides the advantage of simplicity, dual mode of sensing, and more importantly, it employs an inexpensive commercially available probe molecule, which is a significant advantage over other developed sensor systems that uses tedious synthesis protocol for the employed probe in the detection scheme, an impediment for practical applications. Additionally, our sensor system also shows response in complex biological media of serum samples.

Dual responsive salen-type Schiff bases for the effective detection of l-arginine via a static quenching mechanism

The effect of substituents of salen Schiff bases on the detection of l-arginine via a static quenching mechanism is discussed.

Carbon nano-dots as a fluorescent and colorimetric dual-readout probe for the detection of arginine and Cu2+ and its logic gate operation

A new visual fluorescent probe based on carbon nano-dots (CNDs) has been facilely synthesized via one step microwave-assisted pyrolysis and utilized for sequential detection of arginine (Arg) and Cu²⁺ by fluorescent and colorimetric dual-readout assay. The fluorescence of CNDs can be effectively quenched by Arg, and recovered upon addition of Cu²⁺ due to the competitive binding of Arg and Cu²⁺ that leads Arg to escape from the surface of CNDs. The probe displayed high sensitivity and selectivity toward Arg and Cu²⁺ over other analytes with a low detection limit of 0.26 μM and 0.17 μM, respectively. Meanwhile, the CNDs can also give dual responsive signals of a visible color change (yellow-pink-light yellow). According to this phenomenon, an "AND" logic gate based on the novel CNDs has been constructed. More importantly, the probe was also extended to cellular imaging. The proposed method was simple with ease of operation, which demonstrated great potential in bio-sensing, disease diagnosis or environmental monitoring.