A fluorescent probe based on FRET effect between carbon nanodots and gold nanoparticles for sensitive detection of thiourea

Illegal abuse results in the presence of thiourea (TU) in soil, wastewater, and even fruits, which is harmful for the environment and human health. It has urgent practical significance to design an efficient and reliable probe for TU detection. Herein, a sensitive fluorescent probe with off-on response for harmful TU was reported. The probe was designed with fluorescent carbon nanodots (CNDs) and gold nanoparticles (AuNPs) based on fluorescence resonance energy transfer (FRET) effect. Firstly, the CNDs were pre-combined with AuNPs and the fluorescence of CNDs was quenched due to the FRET effect. Upon addition of TU, the fluorescence of CNDs recovered due to the unbinding of CNDs and AuNPs, since the coordination interaction between TU and AuNPs is stronger than the electrostatic interaction among CNDs and AuNPs. Under the optimum parameters, a linear relationship was found between the relative fluorescence intensity of the probe and the concentration of TU in the range of 5.00 × 10^-8-1.00 × 10^-6 M (R² = 0.9958), with the limit of detection (LOD) calculated to be 3.62 × 10^-8 M. This proposed method is easy to operate and has excellent selectivity and sensitivity for TU, which can be effectively applied in environmental water and compound fruit-vegetable juice.

Thiourea sensor development based on hydrothermally prepared CMO nanoparticles for environmental safety

Low-dimensional cobalt oxide codoped manganese oxide nanoparticles (CMO NPs; dia. ~ 25.6nm) were synthesized using the hydrothermal method in alkaline phase. The optical, morphological, and structural properties of CMO NPs were characterized in details using FT-IR, UV/vis., FESEM, XEDS, XPS, TEM, and XRD techniques. Glassy carbon electrode (GCE) was fabricated with a thin-layer of CMO NPs by conducting coating binders for the development of selective and sensitive thiourea (TU) sensors. Electrochemical responses along with higher sensitivity, large-dynamic-range, and long-term stability towards TU were performed by electrochemical I-V approach. The calibration curve was found linear over a wide linear dynamic range (LDR) of TU concentration. From the gradient of the calibration plot, limit of detection (LOD), and sensitivity were calculated as 12.0±0.05pM and 3.3772nAnM^-1cm^-2 respectively. It is an organized route for the development of chemical sensor based on very low-dimensional CMO NPs/GCE using electrochemical reduction phenomena. As far as we know, this report is the maiden publication on highly sensitive TU sensor based on the CMO NPs/GCE. This method could be a pioneer developer in TU sensitive chemical sensor development using doped NPs in the simple I-V method for the important sensor applications with useful doped materials coupled nano-technological systems for environmental safety.

Microfluidic photoinduced chemical oxidation for Ru(bpy)33+ chemiluminescence - A comprehensive experimental comparison with on-chip direct chemical oxidation

For the first time, the analytical figures of merit in detection capabilities of the very less explored photoinduced chemical oxidation method for Ru(bpy)₃²⁺ CL has been investigated in detail using 32 structurally different analytes. It was carried out on-chip using peroxydisulphate and visible light and compared with well-known direct chemical oxidation approaches using Ce(IV). The analytes belong to various chemical classes such as tertiary amine, secondary amine, sulphonamide, betalactam, thiol and benzothiadiazine. Influence of detection environment on CL emission with respect to method of oxidation was evaluated by changing the buffers and pH. The photoinduced chemical oxidation exhibited more universal nature for Ru(bpy)₃²⁺ CL in detection towards selected analytes. No additional enhancers, reagents, or modification in instrumental configuration were required. Wide detectability and enhanced emission has been observed for analytes from all the chemical classes when photoinduced chemical oxidation was employed. Some of these analytes are reported for the first time under photoinduced chemical oxidation like compounds from sulphonamide, betalactam, thiol and benzothiadiazine class. On the other hand, many of the selected analytes including tertiary and secondary amines such as cetirizine, azithromycin fexofenadine and proline did not produced any analytically useful CL signal (S/N=3 or above for 1μgmL^-1 analyte) under chemical oxidation. The most fascinating observations was in the detection limits; for example ofloxacin was 15 times more intense with a detection limit of 5.81×10^-10M compared to most lowest ever reported 6×10^-9M. Earlier, penicillamine was detected at 0.1μgmL^-1 after derivatization using photoinduced chemical oxidation, but in this study, we improved it to 5.82ngmL^-1 without any prior derivatization. The detection limits of many other analytes were also found to be improved by several orders of magnitude under photoinduced chemical oxidation.

A dual-mode signaling response of a AuNP-fluorescein based probe for specific detection of thiourea

By employing fluorescein and AuNPs as energy donors and acceptors, respectively, a novel fluorescence resonance energy transfer (FRET)-based dual-mode sensor for selective recognition and quantitative detection of thiourea was designed and constructed in this study for the first time.

A novel fluorescence probe based on p-acid-Br and its application in thiourea detection

A novel organic fluorescence system was developed to detect thiourea based on p-acid-Br, which in the range of 0.5–1000 nM and with a detection limit of 0.26 nM. And this method provides a new promising platform for clinical analysis.

An on-line spectrophotometric determination of trace amounts of thiourea in tap water, orange juice, and orange peel samples using multi-channel flow injection analysis

In this work, a flow injection analysis (FIA) method was introduced for the determination of trace amounts of thiourea in tap water. This method is based upon the inhibition effect of thiourea on the reaction between meta-cresol purple (MCP) and potassium bromate catalyzed by bromide ions in a sulfuric acid medium. In the presence of thiourea, an induction period appears in the reaction system, and as a result, the absorbance of MCP increases at 525 nm in the FIA manifold. The chemical and FIA variables are studied and optimized using the univariate and Simplex optimization methods. Under the optimum conditions, thiourea can be determined in the range of 0.100-13.0 μg mL(-1). The limit of detection (3σ) for thiourea was found to be 0.0310 μg mL(-1). The relative standard deviations (RSDs) for six replicate determinations of 0.500, 5.00, and 12.0 μg mL(-1) of thiourea were 4.0%, 1.8%, and 1.2%, respectively. The proposed method was also applied for the determination of thiourea in orange juice and orange peel samples with recoveries in the range of 98.0-101%. The analytical speed of the method was calculated to be about 120 sample per hour.

Determination of thiourea in fruit juice by a kinetic spectrophotometric method

A catalytic kinetic method is described for determination of trace levels of thiourea based on its catalytic effect on the oxidation of Janus green (JG) by potassium iodate in hydrochloric acid media. The reaction was monitored by measuring the decrease in absorbance of the dye at 610 nm after 25 min. The effect of some factors on the reaction speed was investigated. The developed method allowed the determination of thiourea in range of 0.01-12.00 mg L(-1) with good precision, accuracy and the detection limit was 0.008 mg L(-1). Most of foreign species do not interfere with the determination. The method was found to be sensitive, selective and was applied to the determination of thiourea in fruit juices and orange peel.

A kinetic method for the determination of thiourea by its catalytic effect in micellar media

A highly sensitive, selective and simple kinetic method was developed for the determination of trace levels of thiourea based on its catalytic effect on the oxidation of janus green in phosphoric acid media and presence of Triton X-100 surfactant without any separation and pre-concentration steps. The reaction was monitored spectrophotometrically by tracing the formation of the green-colored oxidized product of janus green at 617 nm within 15 min of mixing the reagents. The effect of some factors on the reaction speed was investigated. Following the recommended procedure, thiourea could be determined with linear calibration graph in 0.03-10.00 microg/ml range. The detection limit of the proposed method is 0.02 microg/ml. Most of foreign species do not interfere with the determination. The high sensitivity and selectivity of the proposed method allowed its successful application to fruit juice and industrial waste water.

Acidic potassium permanganate as a chemiluminescence reagent—A review

A critical and comprehensive review of acidic potassium permanganate chemiluminescence is presented. This includes discussion on reaction conditions, the influence of enhancers such as polyphosphates, formaldehyde and sulfite, the relationship between analyte structure and chemiluminescence intensity, and the application of this chemistry to determine a wide variety of compounds, such as pharmaceuticals, biomolecules, antioxidants, illicit drugs, pesticides and pollutants. Previous proposals for the nature of the emitting species are re-evaluated in light of recent evidence.

Selective thiourea optical probe based on thiourea-induced removal of chloroacetyl group from chloroacetylamine

A novel chromogenic probe for thiourea, N-chloroacetyl parafuchsin (CAP), was designed and synthesized. The method was based on the reaction of CAP with thiourea, resulting in the initial formation of the S-substituted thioformamidine hydrochloride, which would then undergo the intramolecular amidinolysis to liberate the corresponding amine, and thus leading to an absorbance increase at visible spectral range. Based on this mechanism, a highly selective optical probe for thiourea was developed. Under optimal conditions, absorbance increase (DeltaA) at 562 nm is proportional to thiourea concentration up to 0.2 mmolL(-1) with a detection limit of 2.1 micromolL(-1) (3sigma). Because of the selective removal of chloroacetyl group from CAP by thiourea, there is little interference by other molecules.

Simultaneous detection of monoethanolamine, diethanolamine, and triethanolamine by HPLC with a chemiluminescence reaction and online derivatization to tertiary amine

In this paper we propose a new postcolumn detection method for compounds having primary, secondary, and tertiary amine moieties. The primary and secondary amine are delivatized by a reaction with epichlorohydrin having an epoxy moiety in a reaction coil to yield a tertiary amine with subsequent chemiluminescence detection using [Ru(bpy)3]3+. The liner values of the calibration curves of monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) were 0.02 - 1.0 nmol (r2 = 0.9986), 0.02 - 0.5 nmol (r2 = 0.9993) and 0.1 - 1.0 nmol (r2 = 0.9482), respectively. Also, the detection limits (S/N = 3) of MEA, DEA and TEA were 30, 25 and 40 pmol, respectively. The amount of DEA and TEA in shaving cream (60 microg/20 microL) were found to be 0.3 nmol and 14 nmol, respectively, by the proposed method.

Tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence

This paper critically reviews analytical applications of the chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) and related compounds published in the open literature between mid-1998 and October 2005. Following the introduction, which summarises the reaction chemistry and reagent generation, the review divides into three major sections that focus on: (i) the techniques that utilise this type of detection chemistry, (ii) the range of analytes that can be determined, and (iii) analogues and derivatives of tris(2,2'-bipyridyl)ruthenium(II).

Preliminary Evaluation of Dual Acidic Potassium Permanganate and Tris(2,2′-bipyridyl)ruthenium(II) Chemiluminescence Detection for the HPLC Determination of Papaver somniferum Alkaloids

This paper describes a dual chemiluminescence reagent for the determination of the opiate alkaloids morphine, codeine, oripavine, and thebaine in Papaver somniferum extracts. Detection was achieved using a mixture of acidic potassium permanganate and tris(2,2′-bipyridyl)ruthenium(ii), where the former acted as both the oxidant for the latter and as a chemiluminescence reagent in its own right. The analytes were separated on a C8 column using ion-pairing HPLC. The application of the mixed reagent detection compared favourably with results obtained using standard HPLC methodology. Detection limits for the alkaloids were 10−6, 5 × 10−7, 3 × 10−6, and 2 × 10−6 mol L−1 for morphine, codeine, oripavine, and thebaine, respectively.