Spectrofluorimetric quantification of bromazepam using a highly selective optical probe based on Eu–bromazepam complex in pharmaceutical and serum samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of bromazepam is developed. In phosphate buffer of pH 7.4. The bromazepam enhance the luminescence intensity of the Eu³⁺ ion in Eu³⁺–bromazepam complex at λ_ex = 390 nm. The produced luminescence intensity of Eu³⁺–bromazepam complex is in proportion to the concentration of bromazepam. The working range for the determination of bromazepam is 2.3 × 10⁻⁸ to 6.2 × 10⁻⁷ M with detection limit (LoD) and quantitative detection limit (LoQ) of 3 × 10⁻⁹ and 1.2 × 10⁻⁸ M, respectively. While, the working range, detection limit (LoD) and quantitative detection limit (LoQ) in case of the quantum yield calculations are 3.7 × 10⁻⁸ to 3.4 × 10⁻⁷ M with of 3.4 × 10⁻⁹ and 9.2 × 10⁻⁸ M, respectively. The enhancement mechanism of the luminescence intensity in the Eu³⁺–bromazepam system has been also explained.     

Fluorescence enhancement effect for the determination of DNA with calcein-cetyl trimethyl ammonium bromide system

A new spectrofluorimetric method was developed for the determination of trace amounts of DNA using the calcein as a fluorescent probe. In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer was enhanced by adding DNA at pH 6–7. The interaction between calcein–CTAB and DNA was studied on the basis of this behavior and a new method was developed for determining DNA. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ g L⁻¹ for fsDNA and thermally denatured ctDNA (4.5 × 10⁻⁶ to 9.0 × 10⁻⁵ g L⁻¹). The detection limits (S/N = 3) were 2.0 × 10⁻⁶ and 2.2 × 10⁻⁶ g L⁻¹, respectively. This method was used for determining the concentration of DNA in synthetic samples with satisfactory results.     

A new hydrogen peroxide biosensor based on gold nanoelectrode ensembles/multiwalled carbon nanotubes/chitosan film-modified electrode

Gold nanoelectrode ensembles were produced by electrodeposition using multiwalled carbon nanotubes (MWNTs) as template. A new third generation amperometric biosensor for hydrogen peroxide was developed based on adsorption of horseradish peroxidase (HRP) at the glassy carbon (GC) electrode modified with Au nanoelectrode ensembles/multiwalled carbon nanotubes/chitosan film. The resulting HRP biosensor offered an excellent detection for hydrogen peroxide at −0.11 V with a linear response range of 2.08 × 10⁻⁷ to 7.6 × 10⁻³ M with a correlation coefficient of 0.998, and response time <5 s. The detection limit was 1.02 × 10⁻⁷ M at 3σ. The biosensor displays rapid response, expanded linear response range, and excellent repeatability. The simple and fast fabrication of the sensor makes it superior to other techniques.     

Palladized aluminum electrode covered by Prussian blue film as an effective transducer for electrocatalytic oxidation and hydrodynamic amperometry of N-acetyl-cysteine and glutathione

The mediated oxidation of N-acetyl cysteine (NAC) and glutathione (GL) at the palladized aluminum electrode modified by Prussian blue film (PB/Pd–Al) is described. The catalytic activity of PB/Pd–Al was explored in terms of Fe^III[Fe^III(CN)₆]/Fe^III[Fe^II(CN)₆]¹⁻ system by taking advantage of the metallic palladium layer inserted between PB film and Al, as an electron-transfer bridge. The best mediated oxidation of NAC and GL on the PB/Pd–Al electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 2. The mechanism and kinetics of the catalytic oxidation reactions of the both compounds were monitored by cyclic voltammetry and chronoamperometry. The charge transfer-rate limiting step as well as overall oxidation reaction of NAC or GL is found to be a one-electron abstraction. The values of transfer coefficients α, catalytic rate constant k and diffusion coefficient D are 0.5, 3.2 × 10² M⁻¹ s⁻¹ and 2.45 × 10⁻⁵ cm² s⁻¹ for NAC and 0.5, 2.1 × 10² M⁻¹ s⁻¹ and 3.7 × 10⁻⁵ cm² s⁻¹ for GL, respectively. The modifying layers on the Pd–Al substrate have reproducible behavior and a high level of stability in the electrolyte solutions. The modified electrode is exploited for hydrodynamic amperometry of NAC and GL. The amperometric calibration graph is linear in concentration ranges 2 × 10⁻⁶–40 × 10⁻⁶ for NAC and 5 × 10⁻⁷–18 × 10⁻⁶ M for GL and the detection limits are 5.4 × 10⁻⁷ and 4.6 × 10⁻⁷ M, respectively.     

Electrogenerated chemiluminescence aptamer-based method for the determination of thrombin incorporating quenching of tris(2,2-bipyridine)ruthenium by ferrocene

A novel electrogenerated chemiluminescence (ECL) aptamer-based biosensing method for the determination of thrombin was developed on basis of a structure-switching ECL-dequenching mechanism. A thiolated ss-DNA capture probe, composing of a ss-DNA sequence to adopt two distinct structures-a DNA double strand with a complementary DNA sequence tagged with a ECL signal producer tris(2,2^′-bipyridyl)ruthenium derivative and a DNA duplex with a thrombin-binding aptamer tagged with a ECL-quencher ferrocene (FcDNA), was self-assembled onto surface of a gold electrode. In the presence of thrombin, the aptamer sequence prefers to form the aptamer-thrombin complex and the switch of the binding partners occurs in conjunction with the generation of a strong ECL signal owing to the dissociation of FcDNA. The integrated ECL intensity versus the concentration of thrombin was linear in the range from 2.0 × 10⁻¹⁰ M to 2.0 × 10⁻⁷ M. The detection limit was 6 × 10⁻¹¹ M. The relative standard derivation for 2.0 × 10⁻⁹ M was 5.7% (n = 7). This work demonstrates that the sensitivity and specificity of ECL aptamer-based method for proteins can be greatly improved using quenching ECL signal producer by a chemical quencher such as ferrocene.     

毛细管电泳-安培法测定复方磺胺甲噁唑片中的有效成分

采用毛细管电泳-安培法(CE-AD)同时分离测定了磺胺甲噁唑(sulfamethoxazole,SMZ)、磺胺嘧啶(sulfadiazine,SD)和抗菌增效剂甲氧苄胺嘧啶(trimethoprim,TMP)3种常用磺胺类抗菌药物成分,考察了实验参数对分离、检测体系的影响。在优化实验条件下,以300μm碳圆盘电极作为工作电极,检测电位为1050mV(vs.SCE),在Na2B4O7(13mmol/L)-KH2PO4(18mmol/L)(pH5.8)的缓冲溶液中,分离电压18kV,进样6s,3组分在14min内可实现基线分离。上述3组分浓度分别在5×10-4~5×10-2、5×10-4~0.1和5×10-4~5×10-2g/L范围内与其峰电流强度呈线性关系,检出限达5.1×10-5~8.0×10-5g/L(S/N=3)。该方法已成功应用于复方磺胺甲噁唑片中抗菌活性成分的含量测定,结果令人满意。     

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0 × 10⁻⁶ M and the progress of reaction was followed spectrophotometrically at 525 nm (λ_max of purple-red complex [Ru(CN)₅NRS]³⁻,  = 3.1 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 8.75 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 3.50 × 10⁻⁴ M [nitroso-R-salt], pH 7.00 ± 0.02, ionic strength, I = 0.1 M (KCl), temp 45.0 ± 0.1 °C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t = 15, 20 and 25 min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0 × 10⁻⁷ M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.     

Studies on Intramolecular Charge Transfer Fluorescence Probe and DNA Binding Characteristics

An intramolecular charge transfer fluorescence probe of 4′-N,N-dimethylamino-4-amino-chalcone(DMAC) exhibits characteristics clearly correlated with the polarity of solvents. The interaction of this fluorescence probe with calf thymus DNA has been investigated. Generally, DMAC bound to DNA shows marked changes in fluorescence and absorbance properties compared to the spectral characteristics of the free form in solution phase. In the presence of DNA the fluorescence intensity of DMAC is greatly increased with a large bathochromic shift of excitation and emission wavelengths. A hypochromism in absorption spectrum was also observed. The absorption and fluorescence spectra, salt concentration effect, and KI quenching experiments demonstrate that DMAC molecule as an intercalator is inserted into the base-stacking domain of DNA double helix, and the interaction of the nucleobases with DMAC molecule causes the increase of fluorescence intensity and hypochromism in absorption spectrum. The intrinsic binding constant and the binding site number were estimated to be 7.04 × 10⁶ mol L⁻¹ in base pairs and 0.065, respectively. The I/I₀ vs DNA concentration plot shows a linear range covering 1.98 × 10⁻⁶ to 2.08 × 10⁻⁴ mol L⁻¹ in base pairs which can be used for determining DNA with a detection limit of 6.0 × 10⁻⁷ mol L⁻¹ in base pairs (0.6 μg ml⁻¹).     

Simultaneous determination of hydroquinone and catechol at PASA/MWNTs composite film modified glassy carbon electrode

A poly-amidosulfonic acid and multi-wall carbon nanotubes composite (PASA/MWNTs) modified electrode has been constructed by electropolymerization on glassy carbon electrode (GCE). The electrochemical behaviors of hydroquinone (HQ) and catechol (CC) were investigated using cyclic and differential pulse voltammetries (DPVs) at the prepared electrode. Separation of the reductive peak potentials for HQ and CC was about 120 mV in pH 6.0 phosphate buffer solution (PBS), which makes it suitable for simultaneous determination of these compounds. In the presence of 1.0 × 10⁻⁴ mol L⁻¹ isomer, the reductive peak currents of DPV are proportional to the concentration of HQ in the range of 6.0 × 10⁻⁶ to 4.0 × 10⁻⁴ mol L⁻¹, and to that of CC in the range of 6.0 × 10⁻⁶ to 7.0 × 10⁻⁴ mol L⁻¹. When simultaneously changing the concentration of both HQ and CC, the linear concentration range of HQ (or CC) is 6.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ (or 6.0 × 10⁻⁶ to 1.8 × 10⁻⁴ mol L⁻¹), and the corresponding detection limits are 1.0 × 10⁻⁶ mol L⁻¹. The proposed method has been applied to simultaneous determination of HQ and catechol in water sample, and the results are satisfactory.     

Fabrication of a template-synthesized gold nanorod-modified electrode for the detection of dopamine in the presence of ascorbic acid

Gold nanorods (GNRs) with suitable aspect ratio were synthesized with a template technique and then dispersed in a saturated sodium citrate solution by ultrasonication to form a GNR suspension. A GNR-modified electrode was fabricated using the GNR suspension. The oxidation of dopamine at the GNR/GC electrode exhibited surprisingly high electrocatalytic activity and adsorption-controlled characteristics. Square-wave voltammetry was used to detect dopamine. At the GNR/GC electrode, the linear concentration range of DA is from 1 × 10⁻⁸ M to 1 × 10⁻⁷ M and the detection limit (s/n = 3) is as low as 5.5 × 10⁻⁹ M. The current sensitivity is 3.280 μA/μM, and 1000-fold ascorbic acid (AA) cannot interfere with the determination of DA. All these performances are greatly superior to those of the bare GC electrode.     

A novel fluorescent distinguished probe for Cr (VI) in aqueous solution

Salicylaldehyde rhodamine B hydrazone (SRBH) was developed as a new spectrofluorimetric probe for the selective and sensitive detection of CrO₄²⁻ in acidic conditions. The proposed method was based on the special oxidation reaction between non-fluorescent SRBH by potassium dichromate to produce a highly fluorescent rhodamine B, as a product. Under the optimum conditions described, the fluorescence enhancement at 591 nm was good linearly related to the concentration of CrO₄²⁻ from 1.0 × 10⁻⁸ to 3.0 × 10⁻⁷ M (0.42–12.6 ng mL⁻¹) with a correlation coefficient of R² = 0.9989 (n = 10) and a detection limit of 1.5 × 10⁻⁹ M (0.063 ng mL⁻¹). The relative standard deviation (R.S.D.) was 2.0% (n = 6). The proposed method was also successfully applied to the determination of chromium (VI) in drinking water, river water and synthetic samples.     

Study on the interaction between nucleic acid and Eu3+-oxolinic acid and the determination of nucleic acid using the resonance light scattering technique

At pH 9.75, the resonance light scattering (RLS) intensity of OA–Eu³⁺ system is greatly enhanced by nucleic acid. Based on this phenomenon, a new quantitative method for nucleic acid in aqueous solution has been developed. Under the optimum condition, the enhanced RLS is proportional to the concentration of nucleic acid in the range of 1.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g/ml for herring sperm DNA, 8.0 × 10⁻¹⁰ to 1.0 × 10⁻⁶ g/ml for calf thymus DNA and 1.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g/ml for yeast RNA, and their detection limits are 0.020, 0.011 and 0.010 ng/ml, respectively. Synthetic samples and actual samples were satisfactorily determined. In addition, the interaction mechanism between nucleic acid and OA–Eu³⁺ is also investigated.     

A new Tb-selective fluorescent sensor based on 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide

A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quenching upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M and the detection limit is 1.4 × 10⁻⁷ M. The association constant of the 1:1 complex formation for L–Tb⁺³ was calculated to be 6.01 × 10⁶ M⁻¹, and the fluorescent probe exhibits high selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for Tb(III) ions over a large number of interfering cations.     

Voltammetric determination of N-acetylcysteine using a carbon paste electrode modified with copper(II) hexacyanoferrate(III)

The preparation and electrochemical characterization of a carbon paste electrode modified with copper(II) hexacyanoferrate(III) (CuHCF) as well as its behavior as electrocatalyst toward the oxidation of N-acetylcysteine were investigated. The electrochemical behavior of the modified electrode and the electrooxidation of N-acetylcysteine were explored using sweep linear voltammetry. The best voltammetric response was observed for a paste composition of 20% (w/w) copper(II) hexacyanoferrate(III) complex, acetate buffer solution at pH of 6.0 as the electrolyte and scan rate of 10 mV s^− 1. A linear voltammetric response for N-acetylcysteine was obtained in the concentration range from 1.2 × 10^− 4 to 8.3 × 10^− 4 mol L^− 1, with a detection limit of 6.3 × 10^− 5 mol L^− 1. The proposed electrode is useful for the quality control and routine analysis of N-acetylcysteine in pharmaceutical formulations.     

Oxidative degradation of non-ionic surfactant (TritonX-100) by chromium(VI)

Degradation of polyoxyethylene chain of non-ionic surfactant (TritonX-100) by chromium(VI) has been studied spectrophotometrically under different experimental conditions. The reaction rate bears a first-order dependence on the [Cr(VI)] under pseudo-first-order conditions, [TritonX-100]  [Cr(VI)] in presence of 1.16 mol dm⁻³ perchloric acid. The observed rate constant (k_obs) was 3.3 × 10⁻⁴ to 3.5 × 10⁻⁴ s⁻¹ and the half-life (t_1/2) was 33–35 min for chromium(VI). The effects of total [TritonX-100] and [H⁺] on the reaction rate were determined. Reducing nature of non-ionic TritonX-100 surfactant is found to be due to the presence of –OH group in the polyoxyethylene chain. It was observed that monomeric and non-ionic micelles of TritonX-100 were oxidized by chromium(VI). When [TritonX-100] was less than its critical micelle concentration (cmc) the k_obs values increased from 0.76 × 10⁻⁴ to 1.5 × 10⁻⁴ s⁻¹. As the [TritonX-100] was greater than the cmc, the k_obs values increases from 2.1 × 10⁻⁴ to 8.2 × 10⁻⁴ s⁻¹ in presence of constant [HClO₄] (1.16 mol dm⁻³) at 40 °C. A comparison was made of the oxidative degradation rates of TritonX-100 with different metal ion oxidants. The order of the effectiveness of different oxidants was as follows: permanganate > diperiodatoargentate(III) > chromium(VI) > cerium(IV).     

Kinetic determination of organosulphur ligands by inhibition: Trace determination of cysteine and maleonitriledithiolate (MNDT)

Some organosulphur ligands have been found to inhibit the mercury(II) catalyzed substitution of cyanide in hexacyanoferrate(II) by N-methylpyrazinium ion (Mpz⁺). The inhibitory effect is due to the binding tendency of catalyst Hg²⁺ with these inhibitors. This effect has been used as a basis to develop a kinetic method for the determination of trace amounts of two organosulphur ligands viz. cysteine and MNDT. The reaction was followed spectrophotometrically at 655 nm by measuring the decrease in absorbance of the product [Fe(CN)₅Mpz]²⁻. The influence of the reaction variables has also been studied. A general mechanistic scheme of the indicator reaction system including the role of inhibitor has been proposed and applied to determine the organosulphur ligands. Under the selected experimental conditions cysteine and MNDT have been determined in the range of 2–20 × 10^− 7 M and 5 × 10^− 8 M to 12 × 10^− 7 M respectively in various aqueous samples. The analytical concentration range depends upon the amount of Hg²⁺ present in the indicator reaction and also on the stability of the Hg²⁺-inhibitor complex in question. Under specified conditions, the detection limit for cysteine and MNDT are 2 × 10^− 7 M and 5 × 10^− 8 M respectively. The influences of possible interference by major amino acids, on the determination of cysteine and their limits have been investigated.     

Pulse radiolysis study of ion-species effects on the solvated electron in alkylammonium ionic liquids

The spectra and kinetic behavior of solvated electrons (e_sol⁻) in alkyl ammonium ionic liquids (ILs), i.e. N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEMMA-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEMMA-BF₄), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13-TFSI), and N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P14-TFSI) were investigated by the pulse radiolysis method. The e_sol⁻ in each of the ammonium ILs has an absorption peak at 1100 nm, with molar absorption coefficients of 1.5–2.3×10⁴ dm³ mol⁻¹ cm⁻¹. The e_sol⁻ decayed by first order with a rate constant of 1.4–6.4×10⁶ s⁻¹. The reaction rate constant of the solvated electron with pyrene (Py) was 1.5–3.5×10⁸ dm³ mol⁻¹ s⁻¹ in the various ILs. These values were about one order of magnitude higher than the diffusion-controlled limits calculated from measured viscosities. The radiolytic yields (G-value) of the e_sol⁻ were 0.8–1.7×10⁻⁷ mol J⁻¹. The formation rate constant of e_sol⁻ in DEMMA-TFSI was 3.9×10¹⁰ s⁻¹. The dry electron (e_dry⁻) in DEMMA-TFSI reacts with Py with a rate constant of 7.9×10¹¹ dm³ mol⁻¹ s⁻¹, three orders of magnitude higher than that of the e_sol⁻ reactions. The G-value of the e_sol⁻ in the picosecond time region is 1.2×10⁻⁷ mol J⁻¹. The capture of e_dry⁻ by scavengers was found to be very fast in ILs.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

A novel poly(taurine) modified glassy carbon electrode for the simultaneous determination of epinephrine and dopamine

A novel taurine modified glassy carbon electrode was prepared by electropolymerization method. The electrochemical behaviors of epinephrine (EP) and dopamine (DA) at the modified electrode were studied by cyclic voltammetry. The modified electrode exhibited enhanced sensitivity and excellent electrochemical discrimination to DA and EP. The cathodic peaks of the two species were well-separated with a potential difference of about 390 mV, so the poly(taurine) modified electrode was used for simultaneous voltammetric measurement of EP and DA by differential pulse voltammetry. Under the optimum conditions, the cathodic peak currents were linear to concentrations of EP and DA in the range of 2.0 × 10⁻⁶ to 6.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁶ to 8.0 × 10⁻⁴ mol L⁻¹, respectively. The detection limits for EP and DA were 3.0 × 10⁻⁷ and 1.0 × 10⁻⁷ mol L⁻¹, respectively. Because the oxidation of ascorbic acid (AA) is an irreversible reaction at modified electrode, the interference of AA for determining EP and DA was eliminated. The modified electrode has been satisfactorily used for the simultaneous determination of EP and DA in pharmaceutical injections.     

Design of fluorescent self-assembled multilayers and interfacial sensing for organophosphorus pesticides

This paper details the fabrication of indole (ID) self-assembled multilayers (SAMs) and fluorescence interfacial sensing for organophosphorus (OP) pesticides. Quartz/APES/AuNP/l-Cys/ID film was constructed on l-cysteine modified Quartz/APES/AuNP surface via electrostatic attraction between ID and l-cysteine. Cyclic voltammetry indicates that ID is immobilized successfully on the gold surface. Fluorescence of the Quartz/APES/AuNP/l-Cys/ID film shows sensitive response toward OPs. The fluorescent sensing conditions of the SAMs are optimized that allow linear fluorescence response for methylparathion and monocrotophos over 5.97 × 10⁻⁷ to 3.51 × 10⁻⁶ g L⁻¹ and 3.98 × 10⁻⁶ to 3.47 × 10⁻⁵ g L⁻¹, with detection limit of 6.1 × 10⁻⁸ gL⁻¹ and 3.28 × 10⁻⁶ gL⁻¹, respectively. Compared to bulk phase detection, interfacial fluorescence sensing based on the SAMs technology shows higher sensitivity by at least 2 order of magnitude.