Chemiluminescence of tryptophan and histidine in Ru(bpy)32+-KMnO4 aqueous solution

Highly Sensitive and Selective Detection of L-Tryptophan by ECL Using Boron-Doped Diamond Electrodes

L-tryptophan is an amino acid that is essential to the metabolism of humans. Therefore, there is a high interest for its detection in biological fluids including blood, urine, and saliva for medical studies, but also in food products. Towards this goal, we report on a new electrochemiluminescence (ECL) method for L-tryptophan detection involving the in situ production of hydrogen peroxide at the surface of boron-doped diamond (BDD) electrodes. We demonstrate that the ECL response efficiency is directly related to H2O2 production at the electrode surface and propose a mechanism for the ECL emission of L-tryptophan. After optimizing the analytical conditions, we show that the ECL response to L-tryptophan is directly linear with concentration in the range of 0.005 to 1 µM. We achieved a limit of detection of 0.4 nM and limit of quantification of 1.4 nM in phosphate buffer saline (PBS, pH 7.4). Good selectivity against other indolic compounds (serotonin, 3-methylindole, tryptamine, indole) potentially found in biological fluids was observed, thus making this approach highly promising for quantifying L-tryptophan in a broad range of aqueous matrices of interest.

Copper oxide nanoflowers/poly-l-glutamic acid modified advanced electrochemical sensor for selective detection of l-tryptophan in real samples

The main objective of this research work is to develop a low-cost sensor to detect l-tryptophan (L-tryp) in real sample medium based on a modified glassy carbon electrode. For this, copper oxide nanoflowers (CuONFs) and poly-l-glutamic acid (PGA) were used to modify GCE. The prepared NFs and PGA coated electrode was characterized using field emission scanning electron microscope (FE-SEM) with energy dispersive X-ray (EDX) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Furthermore, the electrochemical activity was performed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent electro-catalytic activity towards L-tryp detection in PBS solution at neutral pH 7.0. Based on the physiological pH condition, the proposed electrochemical sensor can detect L-tryp concentration with a linear range of 1.0 × 10^-4-8.0 × 10^-8 molL^-1 with having a detection limit of 5.0 × 10^-8 molL^-1 and sensitivity of 0.6μA/μMcm². The selectivity of L-tryp was tested with a mixture of salt and uric acid solution at the above conditions. Finally, this strategy demonstrated excellent recovery value in real sample analysis like milk and urine.

Sensitive Electrochemical Detection of Tryptophan Using a Hemin/G-Quadruplex Aptasensor

In this study, we design an electrochemical aptasensor with an enzyme-free amplification method to detect tryptophan (Trp). For the amplified electrochemical signal, the screen-printed electrode was modified with dendritic gold nanostructures (DGNs)/magnetic double-charged diazoniabicyclo [2.2.2] octane dichloride silica hybrid (Fe3O4@SiO2/DABCO) to increase the surface area as well as electrical conductivity, and the hemin/G-quadruplex aptamer was immobilized. The presence of Trp improved the catalytic characteristic of hemin/G-quadruplex structure, which resulted in the efficient catalysis of the H2O2 reduction. As the concentration of Trp increased, the intensity of H2O2 reduction signal increased, and Trp was measured in the range of 0.007–200 nM with a detection limit of 0.002 nM. Compared with previous models, our sensor displayed higher detection sensitivity and specificity for Trp. Furthermore, we demonstrated that the proposed aptasensor successfully determined Trp in human serum samples, thereby proving its practical applicability.

Self-Enhanced Chemiluminescence of Tris(bipyridine) Ruthenium(II) Derivative Nanohybrids: Mechanism Insight and Application for Sensitive Silver Ions Detection

In recent years, self-enhanced tris(bipyridine) ruthenium(II)-based luminescence systems have achieved great development in electrochemiluminescence (ECL) but are seldom mentioned in chemiluminescence (CL). Herein, a self-enhanced CL luminophore with excellent CL behavior was synthesized by covalently cross-linking tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) dichloride ([Ru(dcbpy)₃]Cl₂) with branched polyethylenimine (BPEI) in one molecule (BPEI-Ru(II)), which then self-assembled into nanoparticles (BRuNPs). The nanoparticles exhibited stable and strong CL emission with potassium persulfate (K₂S₂O₈) as the oxidant. After the redox reaction between K₂S₂O₈ and BRuNPs, and the subsequent intramolecular electron-transfer reaction, excited state luminophores were generated to emit light. This self-enhanced CL system shortened the electron transfer distance and reduced energy loss, thus improving the luminous efficiency. In addition, the CL lifetime of BRuNPs/K₂S₂O₈ was longer than classical luminophores such as N-(4-aminobutyl)-N-ethylisoluminol (ABEI), indicating the potential application of this system in CL imaging. Surprisingly, Ag⁺ was found to greatly improve the CL efficiency of BRuNPs/K₂S₂O₈ by catalyzing the decomposition of K₂S₂O₈ to generate SO₄^•-. On the basis of the enhancement effect of Ag⁺, a simple and rapid CL method was proposed for Ag⁺ detection. The chemosensor showed a wide linear range from 25 to 3000 nM and low detection limit of 9.03 nM, as well as good stability and excellent selectivity. More importantly, this result indicated that Ag⁺ can be used as a coreaction accelerator to develop a ternary self-enhanced CL system, BRuNPs/K₂S₂O₈/Ag⁺.

Electrochemical Sensor for Rapid and Sensitive Detection of Tryptophan by a Cu2O Nanoparticles-Coated Reduced Graphene Oxide Nanocomposite

In this paper, a nanocomposite of cuprous oxide and electrochemically reduced graphene oxide (Cu₂O–ERGO) was prepared by a simple and low-cost method; hereby, a new method for the electrochemical determination of tryptophan (Trp) by this composite modified glassy carbon electrode (GCE) is proposed. The prepared materials and modified electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and cyclic voltammetry (CV). The results showed that Cu₂O–ERGO/GCE had good electrocatalytic activity for Trp. The effects of supporting electrolyte, scanning rate, accumulation potential, and accumulation time on the determination of Trp were studied. Under the optimum experimental conditions, Trp was quantitatively analyzed by square-wave voltammetry (SWV). The oxidation peak current of Trp had a good linear relationship with its concentration in the range of 0.02–20 μM, and the detection limit was 0.01 μM (S/N = 3). In addition, the modified electrode has high sensitivity, good repeatability, and long-term stability. Finally, the proposed method has been successfully applied in the determination of Trp concentration in practical samples.

Construction of a highly sensitive signal-on aptasensor based on gold nanoparticles/functionalized silica nanoparticles for selective detection of tryptophan

In this work, a highly sensitive, low-cost, and label-free aptasensor based on signal-on mechanisms of response was developed by immobilizing the aptamer on gold nanoparticles (AuNPs)/amine-functionalized silica nanoparticle (FSN)/screen-printed electrode (SPE) surface for highly selective electrochemical detection of tryptophan (Trp). The hemin (Hem), which interacted with the guanine bases of the aptamer, worked as a redox indicator to generate a readable electrochemical signal. The changes in the charge transfer resistance have been monitored using the voltammetry and electrochemical impedance spectroscopic (EIS) techniques. The peak current of Hem linearly increased with increasing concentration of Trp, in differential pulse voltammetry, from 0.06 to 250 nM with a detection limit of 0.026 nM. Also, the results obtained from EIS studies showed that the Trp was detected sensitively with the fabricated aptasensor in the range of 0.06-250 nM. The detection limit is 0.01 nM, much lower than that obtained by most of the reported electrochemical methods. The usage of aptamer as a recognition layer led to a sensor with high affinity for Trp, compared with control amino acids of tyrosine, histidine, arginine, lysine, valine, and methionine. The usability of the aptasensor was successfully evaluated by the determination of Trp in a human blood serum sample. Thus, the sensor could provide a promising plan for the construction of aptasensors. Graphical abstract Schematic outline the principle for tryptophan aptasensing.

A novel strategy to analyze L-tryptophan through allosteric Trp repressor based on rolling circle amplification

Rolling circle amplification (RCA) has been considered as a powerful tool for nucleic acids detection. Here, a novel repressor-RCA-based method for L-tryptophan (L-Trp) detection was developed. This method utilizes the specific interaction between the RCA circular template and the Trp repressor protein (TrpR) involved in trp operon of Escherichia coli (E. coli). In the absence of L-Trp, the TrpR protein could not bind to the RCA template, and the RCA process can be continued. When L-Trp is present, the activated TrpR will bind to the operon sequence on the RCA template and inhibit the RCA reaction. Thus, the concentration of L-Trp is correlated directly with the fluorescent RCA signals. We succeeded in detecting L-Trp in a single step in simple homogeneous reaction system. The detection limit was estimated to be 0.77 μM (S/N=3) with good linearity. The method can unambiguously distinguish L-Trp from other 19 standard amino acids and L-Trp analogs. This strategy is also promising for detecting many small molecules such as other amino acids and carbohydrates.

Enhanced chemiluminescence CdSe quantum dots by histidine and tryptophan

The enhancing effect of histidine and tryptophan on chemiluminescence (CL) of CdSe quantum dots (QDs)-H2O2 system was studied. This reaction is based on the catalytic effect of amino acids, causing a significant increase in the light emission, as a result of the reaction of quantum dots (QDs) with hydrogen peroxide. In the optimum conditions, this method was satisfactorily described by linear calibration curve in the range of 0.66-35.5 μM and 0.83-35.1 μM for histidine and tryptophan, respectively. The effect of various parameters such as concentration of CdSe QDs, concentration of H2O2 and concentration of imidazole on the intensity of CL system were studied. The main experimental advantage of the proposed method is it's selective to two amino acids compared with other amino acids.

A sensitive flow injection chemiluminescence method for the determination of progesterone

A sensitive flow injection (FI) chemiluminescence (CL) method was developed for the determination of trace amounts of progesterone. This method was based on the luminescent properties of the tris(1,10-phenanthroline) ruthenium(II) - potassium permanganate (KMnO4 ) - progesterone in acidic medium sensitized by Na2 SO3 . With the peak height as a quantitative parameter applying optimum conditions, the relative CL intensity was linear with progesterone concentration in the range of 1.0 × 10(-10) ∼ 6.0 × 10(-9) g·ml(-1) and 6.0 × 10(-9) ∼ 4.0 × 10(-8) g·ml(-1) with a detection limit of 7.1 × 10(-11) g·ml(-1) . The relative standard deviation (RSD) was 2.79% for 1.0 × 10(-8) g·ml(-1) progesterone (n = 11). The proposed method held low detection limit and was successfully applied to determination of progesterone in pharmaceutical preparations. The possible CL reaction mechanism was also discussed.