Investigation on the chemiluminescence reaction of luminol–H2O2–S2−/R–SH system

Ultrasensitive PD-L1-Expressing Exosome Immunosensors Based on a Chemiluminescent Nickel-Cobalt Hydroxide Nanoflower for Diagnosis and Classification of Lung Adenocarcinoma

Programmed death ligand-1 (PD-L1)-expressing exosomes are considered a potential marker for diagnosis and classification of lung adenocarcinoma (LUAD). There is an urgent need to develop highly sensitive and accurate chemiluminescence (CL) immunosensors for the detection of PD-L1-expressing exosomes. Herein, N-(4-aminobutyl)-N-ethylisopropanol-functionalized nickel-cobalt hydroxide (NiCo-DH-AA) with a hollow nanoflower structure as a highly efficient CL nanoprobe was synthesized using gold nanoparticles as a "bridge". The resulting NiCo-DH-AA exhibited a strong and stable CL emission, which was ascribed to the exceptional catalytic capability and large specific surface area of NiCo-DH, along with the capacity of AuNPs to facilitate free radical generation. On this basis, an ultrasensitive sandwich CL immunosensor for the detection of PD-L1-expressing exosomes was constructed by using PD-L1 antibody-modified NiCo-DH-AA as an effective signal probe and rabbit anti-CD63 protein polyclonal antibody-modified carboxylated magnetic bead as a capture platform. The immunosensor demonstrated outstanding analytical performance with a wide detection range of 4.75 × 103-4.75 × 108 particles/mL and a low detection limit of 7.76 × 102 particles/mL, which was over 2 orders of magnitude lower than the reported CL method for detecting PD-L1-expressing exosomes. Importantly, it was able to differentiate well not only between healthy persons and LUAD patients (100% specificity and 87.5% sensitivity) but also between patients with minimally invasive adenocarcinoma and invasive adenocarcinoma (92.3% specificity and 52.6% sensitivity). Therefore, this study not only presents an ultrasensitive and accurate diagnostic method for LUAD but also offers a novel, simple, and noninvasive approach for the classification of LUAD.

On-site and high-resolution spectrophotometric measurement of total dissolved sulfide in natural waters

Reliable high-resolution data is essential for understanding the aquatic sulfur biogeochemical processes. However, the accurate quantification of total dissolved sulfide (TDS) remains challenging due to its low concentration and vulnerability to oxidation. Furthermore, the frequency and the spatial coverage of TDS measurements are constrained by the cost of the laboratory analysis. In this study, an automated portable system was developed for on-site real-time measurement of trace TDS in natural waters. This system was based on the classic methylene blue (MB) spectrophotometric assay combined with on-line solid phase extraction (SPE) and flow injection analysis (FIA). A commercially available weak-cation-exchange cartridge was used as the SPE sorbent. Experimental parameters affecting the performance of the proposed system were optimized. Under the optimized conditions, linear calibration range of 0.02-2.50 μmol L^-1 was obtained with a sample loading volume of 5.0 mL and a sample throughput of 12 h^-1. The limit of detection could be lowered to 0.003 μmol L^-1 by pre-concentrating 10.0 mL sample. The precision, determined as the relative standard deviation (RSD), was <2.75 % (n = 11) and the recoveries from spiked samples ranged from 54.4 % to 97.5 % with RSDs of 1.1-2.3 % (n = 3). Furthermore, the FIA-SPE-MB system was successfully deployed in the Taihu Lake for continuous 48 h monitoring of variations in TDS, demonstrating the applicability of this system for on-site TDS measurement in natural waters.

Improving the measurement of total dissolved sulfide in natural waters: A new on-site flow injection analysis method

Total dissolved sulfide (TDS) plays multiple important roles in the aquatic environments. However, the determination of trace levels of TDS in natural waters is challenging because TDS is vulnerable to oxidation and volatilization. In this study, a fully automated flow injection analysis spectrophotometric system, incorporating a hollow fiber membrane contactor (HFMC) and a long path length liquid waveguide capillary cell, was fabricated to facilitate the on-site measurement of trace TDS in natural waters. The HFMC was used for matrix separation and analyte preconcentration. The measurement was based on the reaction of sulfide and N,N-dimethyl-p-phenylenediamine in the presence of FeCl₃ under acidic conditions to yield methylene blue (MB). The proposed method was highly sensitive, with detection and quantification limits of 0.57 and 1.90 nmol L^-1, respectively. The linear working range was from 1.90 to 150 nmol L^-1, with a correlation coefficient of 0.9995. The repeatability, expressed as the relative standard deviation, was less than 0.86% (n = 15) and the recoveries varied from 76.2 ± 0.1% to 103.9 ± 0.6% (n = 3) for spiked samples. This method was applied to conduct a field analysis of TDS in a reservoir, giving results aligned with those obtained using a standard MB method. This work demonstrates that the new method for determining TDS was effective for both laboratory analysis and on-site measurement.

Gold-activated luminol chemiluminescence for the selective determination of cysteine over homocysteine and glutathione

This work reports a chemiluminescence assay for the highly selective determination of cysteine in biological fluids without separation techniques. The method is based on the ability of cysteine to selectively enhance the metal-catalyzed chemiluminescence generated by the oxidation of luminol from gold tetrachloride anions under alkaline conditions. The selectivity of the method stems from the fact that, under strongly alkaline conditions, the formation of the four-membered ring transition state of cysteine is less favorable as compared to the formation of the respective 5- and 9- membered ring transition states of homocysteine and glutathione, respectively. These transition states exert stronger hindrance and hydrophobic interactions repelling the negatively charged luminol dianion and possibly exhibit lower reducing ability for dissolved oxygen, towards the formation of superoxide radicals, thus reducing the oxidation of luminol. Under the optimum experimental conditions, the linear range of the method extended from 0.5 to 20 μΜ while cysteine could be determined at concentrations as low as 0.5 μM, with good reproducibility (<3.5%) and recoveries between 80 and 93% in artificial and real biological fluids.

Determination of nanomolar dissolved sulfides in water by coupling the classical methylene blue method with surface-enhanced Raman scattering detection

In this study, we proposed a novel method for the determination of nanomolar dissolved sulfides, including H₂S, HS^-, and S^2- (defined as S(-II)) in water by coupling the classical methylene blue (MB) method with surface-enhanced Raman spectroscopy (SERS) detection. Overall, the following analytical procedures were employed: i) precipitation of S(-II) as zinc sulfide, ii) centrifugation to collect zinc sulfide, iii) derivatization of S(-II) to MB by the reaction with N, N-dimethyl-p-phenylenediamine in the presence of FeCl₃ under acidic conditions, and iv) SERS detection. Parameters affecting the derivatization and SERS detection were optimized. Under the optimized conditions, a linear range of 12.3 nmol/L-200 nmol/L for S(-II) was obtained with a correlation coefficient (R²) of 0.99. Limits of detection and quantification of the developed method were estimated to be 3.7 nmol/L and 12.3 nmol/L, respectively. In addition, the proposed method demonstrated excellent tolerance to coexisting substances, such as NO₂^-, NO₃^-, SO₃^2-, and other common ions. The proposed method demonstrates immense promise for the determination of nanomolar S(-II) in surface waters and wastewater.

Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System

Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH₂) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (K_SV ~ 10⁸-10¹⁰ M^-1) was calculated to be ca. 10⁴ times more for surface quoted NPs in comparison with BSA-NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH₂ captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs. Graphical Abstract Energy transfer from excited luminol to metal nanoparticles is strongly modulated in presence of serum albumins.

N-(Aminobutyl)-N-(ethylisoluminol)-functionalized gold nanoparticles on cobalt disulfide nanowire hybrids for the non-enzymatic chemiluminescence detection of H2O2

N-(Aminobutyl)-N-(ethylisoluminol) (ABEI)-functionalized gold nanoparticles (AuNPs) on cobalt disulfide nanowires (ABEI/AuNPs/CoS2 NWs) are rapidly synthesized through a microwave-assisted reduction of chloroauric acid (HAuCl4) on CoS2 NWs with ABEI. The obtained nanohybrids with enhanced chemiluminescence are exploited for the non-enzymatic detection of H2O2.

Quantification of glutathione in single cells from rat liver by microchip electrophoresis with chemiluminescence detection

Glutathione (GSH) is a major endogenous antioxidant that has a central role in cellular defense against toxins and free radicals. Rapid and accurate detection of GSH content in single cells is important to the early diagnosis of disease and biomedical research. In this work, a novel method based on microchip electrophoresis chemiluminescence (MCE-CL) detection was developed for the quantification of glutathione (GSH) in single cells from rat liver. The detection of GSH is based on the strong sensitization of mercapto compound to luminol-H₂O₂CL system. The injection, localization, and membrane dissolution of single cell were simply and rapidly carried out on the microchip by direct electric field force, which did not require any additional membrane dissolution reagent. Under optimized experimental conditions, single cell assay was achieved within 2min. The peak area of the GSH was taken as quantification of GSH, and a good linear relationship of GSH concentration to peak area in the range of 3.0 × 10^-6M to 6.0 × 10^-4M was obtained. The detection limit for GSH is 9.6 × 10^-7M, calculated by S/N = 3. The measured GSH content in single cells from rat liver (n = 10) ranged from 7.8fmol to 13.fmol with a mean value of 10.8fmol.

Determination of the binding constant of specific interactions and binding target concentration simultaneously using a general chemiluminescence method

The measurement of the binding constant of specific interactions and concentration of a target is of considerable importance in clinical diagnosis, therapy, bioassays and drug design.

Intracellular detection of Cu(2+) and S(2-) ions through a quinazoline functionalized benzimidazole-based new fluorogenic differential chemosensor

A new quinazoline functionalized benzimidazole-based fluorogenic chemosensor H3L is synthesized and fully characterized by conventional techniques including single crystal X-ray analysis. It acts as a highly selective colorimetric and fluorescence sensor for Cu(2+) ions in DMF/0.02 M HEPES (1 : 1, v/v, pH = 7.4) medium. Reaction of H3L with CuCl2 forms a mononuclear copper(ii) [Cu(Cl)(H2L)(H2O)] (H2L-Cu(2+)) complex which is characterized by conventional techniques and quantum chemical calculations. Electronic absorption and fluorescence titration studies of H3L with different metal cations show a distinctive recognition only towards Cu(2+) ions even in the presence of other commonly coexisting ions such as Li(+), Na(+), K(+), Mg(2+), Ca(2+), Fe(2+), Fe(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+) and Hg(2+). Moreover, H2L-Cu(2+) acts as a metal based highly selective and sensitive chemosensor for S(2-) ions even in the presence of other commonly coexisting anions such as F(-), Cl(-), Br(-), I(-), SO4(2-), SCN(-), AcO(-), H2PO4(-), PO4(3-), NO3(-), ClO4(-), NO2(-), HSO4(-), HSO4(2-), S2O3(2-), S2O8(2-), CN(-), CO3(2-) and HCO3(-) in DMF/0.02 M HEPES (1 : 1, v/v, pH = 7.4) medium. Quantification analysis indicates that these receptors, H3L and H2L-Cu(2+), can detect the presence of Cu(2+) and S(2-) ions at very low concentrations of 1.6 × 10(-9) M and 5.2 × 10(-6) M, respectively. The propensity of H3L as a bio-imaging fluorescent probe for detection of Cu(2+) ions and sequential detection of S(2-) ions by H2L-Cu(2+) in Dalton lymphoma (DL) cancer cells is also shown.

Pyridine-biquinoline-metal complexes for sensing pyrophosphate and hydrogen sulfide in aqueous buffer and in cells

Herein, we report a new pyridine-biquinoline-derivative fluorophore L for effectively sensing pyrophosphate (PPi) and monohydrogen sulfide (HS(-)) in aqueous buffer and in living cells. L could selectively coordinate with metal ions (M(n+)) in Groups IB and IIB to form L-M(n+) complexes with 1:1 stoichiometry, resulting in fluorescence quenching via photoinduced electron transfer (PET) mechanism. L-Zn(2+) complex was applied to competitively coordinate with PPi to form a new "ate"-type complex, turning on the fluorescence by a 21-fold-increase. The limit of detection (LOD) of this assay for PPi detection in aqueous buffer is 0.85 μM. L-Cu(2+) complex was applied for highly selective detection of HS(-) with an excellent sensitivity by 25-fold decomplexation-induced fluorescence increase. LOD of L-Cu(2+) complex for HS(-) detection in aqueous buffer is 2.24 μM. With the in vitro data obtained, we successfully applied these two complexes for sequential imaging Zn(2+) and PPi, Cu(2+) and HS(-) in living cells, respectively. Since PPi and HS(-) occur in vascular calcification in positive correlation, our multifunctional probe L might help doctors to more precisely diagnose this disease in vivo in the future. For example, we could use radioactive tracer L-(64)Cu for qualitative and quantitative positron emission tomography/computed tomography (PET/CT) imaging of HS(-) in vivo.

Determination of sodium sulfide based on electrochemiluminescence of rhodamine B at a SWNT modified glassy carbon electrode

Rhodamine B (RhB) was covalently linked with SWNTs through different linkages and modified on a glassy carbon (GC) electrode to detect sodium sulfide with good reproducibility and stability.

Development of a generic assay for the determination of total trihydroxybenzoate derivatives based on gold-luminol chemiluminescence

A selective assay for the determination of one of the most important class of phenolic compounds, namely trihydroxybenzoates (monomeric and polymeric compounds having at least one gallate moiety) based on their enhancing effect on the chemiluminogenic reaction between gold ions and luminol is described for the first time. In the presence of trihydroxybenzoate derivatives, the light emission generated when alkaline luminol is oxidized by gold ions is amplified several orders of magnitude compared to other common phenolic compounds which exhibit minor reactivity or no reactivity at all (e.g. hydroxycinnamates, flavonols, benzenediols). Based on this property, the experimental conditions were optimized in order to enable the determination of total trihydroxybenzoates in complex mixtures without resorting to separation techniques. The method was applied to samples of different composition (teas, herbal infusions and wines) with satisfactory analytical features yielding detection limits at the 10(-7) mol L(-1) level, intra-day precision of 3.1%, inter-day precision less than 10% and recoveries between 88.7 and 97.6%. The strengths and weaknesses of the method were identified and discussed in relation to its application in real samples.

Silver nanoparticle-initiated chemiluminescence reaction of luminol-AgNO3 and its analytical application

Ag(+) has been regarded as an inert chemiluminescent oxidant. In this work, it was found that in the presence of silver nanoparticles (AgNPs), AgNO(3) could react with luminol to produce strong chemiluminescence (CL). The AgNPs with smaller size could initiate stronger CL emission. To investigate the CL mechanism of the AgNPs-luminol-AgNO(3) system, the UV-visible spectra and the CL spectrum of the CL system were obtained. The CL reaction mechanism involving catalysis was proposed. Compared with the reported nanoparticles-luminol-H(2)O(2) CL system, the AgNPs-luminol-AgNO(3) CL system has the advantages of low background and good stability. Moreover, the new CL system was used in immunoassay for IgG.

Direct introduction of water sample in multisegmented flow-injection analysis for sulfide determination

The present paper describes an inline flow-injection analysis system for the determination of sulfide in water samples, exploiting the Fischer reaction. Water samples were collected and introduced into a reactor of the FIA system. The sulfide released, after sample acidification, was carried out with a nitrogen gas flow and mixed with N,N diethyl-p-phenylenediamine (DEPD) solution in the presence of Fe(III). The blue dye formed was measured in the wavelength range between 672-679 nm. An evaluation of the effects of chemical and flow factors was performed using the factorial design of two levels, while optimization was accomplished by a Doehlert matrix. The system presented two linear-response ranges: the first of 0.433 to 400 µg L(-1) and the second of 400 to 3500 µg L(-1). The detection and quantification limit were found to be 0.130 and 0.433 µg L(-1), respectively, while the sample throughput was 12 h(-1). The precision was evaluated as the relative standard deviation (n = 10); for 50 and 100 µg L(-1) sulfide it was found to be 1.9 and 2.3%, respectively. The method showed satisfactory selectivity regarding the main interference present in environmental samples. The accuracy of the method was successfully evaluated in environmental water samples after a comparison with a literature reference method.

Determination of intracellular glutathione and glutathione disulfide using high performance liquid chromatography with acidic potassium permanganate chemiluminescence detection

Measurement of glutathione (GSH) and glutathione disulfide (GSSG) is a crucial tool to assess cellular redox state. Herein we report a direct approach to determine intracellular GSH based on a rapid chromatographic separation coupled with acidic potassium permanganate chemiluminescence detection, which was extended to GSSG by incorporating thiol blocking and disulfide bond reduction. Importantly, this simple procedure avoids derivatisation of GSH (thus minimising auto-oxidation) and overcomes problems encountered when deriving the concentration of GSSG from 'total GSH'. The linear range and limit of detection for both analytes were 7.5 × 10(-7) to 1 × 10(-5) M, and 5 × 10(-7) M, respectively. GSH and GSSG were determined in cultured muscle cells treated for 24 h with glucose oxidase (0, 15, 30, 100, 250 and 500 mU mL(-1)), which exposed them to a continuous source of reactive oxygen species (ROS). Both analyte concentrations were greater in myotubes treated with 100 or 250 mU mL(-1) glucose oxidase (compared to untreated controls), but were significantly lower in myotubes treated with 500 mU mL(-1) (p < 0.05), which was rationalised by considering measurements of H(2)O(2) and cell viability. However, the GSH/GSSG ratio in myotubes treated with 100, 250 and 500 mU mL(-1) glucose oxidase exhibited a dose-dependent decrease that reflected the increase in intracellular ROS.

Enhancement of chemiluminescence of the KIO4-luminol system by gallic acid, acetaldehyde and Mn2+: application for the determination of catecholamines

Chemiluminescence (CL) from the oxidation of luminol with potassium periodate in strong alkaline solutions was greatly enhanced by the combined effect of gallic acid, acetaldehyde and Mn(2+). The CL spectra exhibited only one emission band at 425 nm, indicating 3-aminophthalate as the emitting species. Various scavengers for superoxide anion, hydroxyl radical and singlet oxygen quenched the CL emission very efficiently (74-100%), suggesting the possible involvement of these reactive oxygen species (ROS) in the CL reactions. It is postulated that oxidation of gallic acid and acetaldehyde by periodate catalyzed by Mn(2+) generates these ROS, which then react with luminol to enhance the CL emission. We also found that the enhanced CL emission was strongly inhibited by catecholamines, probably because of their effective scavenging of ROS. Based on this observation, a simple, rapid and sensitive new CL method was developed for the determination of catecholamines. The detection limits (3sigma) for dopamine, l-dopa, norepinephrine and epinephrine were 0.63, 1.37, 0.56 and 14.3 nmol/L, respectively. The linear range was 1-10 nmol/L; relative standard deviations were 0.71-1.34% for 0.1 micromol/mL catecholamines. This CL method was applied to the determination of catecholamines in pharmaceutical injections with satisfactory results.

Flow-injection determination of cysteine in pharmaceuticals based on luminol-persulphate chemiluminescence detection

A flow injection (FI) method is reported for the determination of l-cysteine, based on its enhancement on chemiluminescence (CL) emission of luminol oxidized by sodium persulphate in alkaline solution. The calibration graph was linear over the range 1.0 x 10(-9)-5.0 x 10(-7) mol/L (r(2) = 0.9992), with relative standard deviations (RSDs) in the range 1.1-2.3% (n = 4). The limit of detection (3 sigma blank) was 5.0 x 10(-10) mol/L with a sample throughput of 120/h. The method was applied to pharmaceuticals and the results obtained were in reasonable agreement with the amount labelled. The proposed method was also applied to cysteine in synthetic amino acid mixtures. Calibration graphs of N-acetylcysteine and glutathione over the range 1.0-50 x 10(-8) and 0.5-7.5 x 10(-7) mol/L were also established (r(2) = 0.998 and 0.9986) with RSDs in the range 1.0-2.0% (n = 4), and the limits of detection (3 sigma blank) were 5.0 x 10(-9) and 1.0 x 10(-8) mol/L, respectively.