Analysis of Gizzerosine in Foodstuffs by HPLC Involving Pre-column Derivatization with o-Phthaldialdehyde.

Gizzerosine [2-amino-9-(4-imidazolyl)-7-azanonanoic acid] is a toxic amino acid formed from histamine and lysine at high temperatures, and may be present in foodstuffs (e.g., fishmeal and meat-bone meal) for animals including cats and dogs. Here we developed a simple, rapid, sensitive, specific, and automated method for the analysis of gizzerosine in foodstuffs by high-performance liquid chromatography (HPLC) involving pre-column derivatization with o-phthaldialdehyde (OPA) in the presence of N-acetylcysteine (instead of the usual 2-mercaptoethanol or ethanethiol reagent). OPA reacted immediately (within 1 min) with gizzerosine in an autosampler at room temperatures (e.g., 20-25 °C), and their derivative was directly injected into the HPLC column. The highly fluorescent gizzerosine-OPA derivative was well separated from the OPA derivatives of all natural amino acids known to be present in physiological fluids (e.g., plasma), proteins and foodstuffs, and was detected at an excitation wavelength of 340 nm and an emission wavelength of 450 nm. The total time for chromatographic separation (including column regeneration) was 20 min per sample rather than 40 min and longer in previous HPLC methods. The detection limit for gizzerosine was at least 6 pmol/ml in an assay solution (HPLC vial) or at least 0.09 pmol per injection into the HPLC column. The analysis of gizzerosine was linear between 1 and 100 pmol per injection. When gizzerosine was extracted from foodstuffs, its detection limit was at least 875 pmol/g foodstuff or at least 0.21 mg/kg foodstuff. Our routine HPLC technique does not require any cleanup of samples or the OPA derivatization products (including the OPA-gizzerosine adduct), and is applicable for the analysis of gizzerosine in both foodstuffs and animal tissues.

Flavipin from fungi as a potential inhibitor of rheumatoid arthritis signaling molecules.

Flavipin, a fungal lower molecular weight biomolecule (MW 196.16 g/mol), has not been yet extensively studied for beneficial preclinical and clinical applications. In recent years, various preclinical mouse models including adjuvant-induced arthritis (AIA) were employed to understand mechanisms associated with Rheumatoid arthritis (RA) and to develop new therapeutic drugs. In the current study, we studied the inhibitory effect of Flavipin on major signaling molecules involved in the inflammatory response during RA using both in-silico virtual interaction and in vivo mouse model of AIA. Our in-silico results clarified that Flavipin interacts with the tumor necrosis factor alpha (TNF-α) through conventional hydrogen binding (H-H) at one of TNF-α critical amino acids tyrosine residues, Tyr119, with binding energy (b.e.) -5.9. In addition, Flavipin binds to ATP-binging sites of the Jesus kinases, JAK1, JAK2 and JAK3, through H-H (b. e. between -5.8 and -6.1) and then it may inhibit JAKs, regulators of RA signaling molecules. Moreover, our molecular dynamics stimulation for the docked TNF-α/Flavipin complex confirmed the specificity and the stability of the interaction. In vitro, Flavipin is not toxic to normal cells at doses below 50 µM (its IC50 in normal fibroblast cell line was above 100 µM). However, in vivo, the arthritis score and hind paw oedema parameters were modulated in Flavipin treated mice. Consistent with the in-silico results the levels of the TNF-α, the nuclear transcription factor kappaB (NF-κB) and the signal transduction and activator of transcription (STAT3, downstream of JAKs) were modulated at joint tissues of the hind-paw of Flavipin/AIA treated mice. Our data suggest Flavipin as a potential therapeutic agent for arthritis can inhibit RA major signaling molecules.

O-phthalaldehyde based quantification of polysaccharide modification in conjugate vaccines.

Polysaccharide-based vaccines cannot stimulate long-lasting immune response in infants due to their inability to elicit a T-cell-dependent immune response. This has been addressed using conjugation technology, where conjugates were produced by coupling a carrier protein to polysaccharides using different conjugation chemistries, such as cyanylation, reductive amination, ethylene diamine reaction, and others. Many glycoconjugate vaccines that are manufactured using different conjugation technologies are already in the market for neonates, infants and young children (e.g., Haemophilus influenzae type-b, Streptococcus pneumoniae and Neisseria meningitidis vaccines), and all of them elicit a T-cell dependent immune response. To manufacture glycoconjugate vaccines, the capsular polysaccharide is first activated by converting its hydroxyl groups to aldehyde-, cyanyl-, or cyanate ester groups, depending on the conjugation chemistry selected. The oxidized and reduced aldehyde functional groups of the polysaccharides are subsequently reacted with the amino groups of carrier protein by reductive amination to form a stable amide bond. In CDAP-based conjugation, the polysaccharide -OH groups are activated to form cyanyl-, or cyanate ester groups to react with the amino groups of carrier protein and forms an isourea bond. Understanding the extent of polysaccharide activation/modification is essential since it directly influences the molar mass of the conjugate, its stability, and the immunogenicity of the product. Reported methods are available to estimate the aldehyde groups of polysaccharides generated by reductive amination. However, no method is available to quantify the cyanyl or cyanate ester (-OCN) groups generated by cyanylation with 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP). We report a novel strategy using an O-phthalaldehyde (OPA) derivatization process followed by size-exclusion chromatography (SEC) high-performance liquid chromatography (HPLC) separation and UV detection. The cyanate ester groups on the activated polysaccharide directly reveal the extent of polysaccharide activation/modification and the residual activated groups in the purified conjugates. This method would be useful for conjugate vaccine manufacturing using CDAP chemistry.

Automated method for quantification of 20 amino acids in cell culture media during biopharmaceutical development.

Herein, a step-by-step protocol for simultaneous detection of 20 amino acids commonly present in cell culture media is described. The protocol facilitates detection of both primary and secondary amino acids through a two-step precolumn derivatization strategy using ortho-phthalaldehyde and 9-fluorenylmethyl chloroformate as derivatizing agents. The separation of derivatized amino acids with varying hydrophobicity is achieved through reverse-phase chromatography. The amino acids are simultaneously detected in a single workflow through the use of Variable Wavelength Detector at 338 and 262 nm. The protocol is applicable for both mammalian and bacterial cell culture matrices with an option for automation of precolumn derivatization.

In Vitro Permeability Study of Homotaurine Using a High-Performance Liquid Chromatography with Fluorescence Detection Pre-Column Derivatization Method.

Homotaurine (HOM) is considered a promising drug for the treatment of Alzheimer's and other neurodegenerative diseases. In the present work, a new high-performance liquid chromatography with fluorescence detection (HPLC-FLD) (λex. = 340 nm and λem. = 455 nm) method was developed and validated for the study of substance permeability in the central nervous system (CNS). Analysis was performed on a RP-C18 column with a binary gradient elution system consisting of methanol-potassium phosphate buffer solution (pH = 7.0, 0.02 M) as mobile phase. Samples of homotaurine and histidine (internal standard) were initially derivatized with ortho-phthalaldehyde (OPA) (0.01 M), N-acetylcysteine (0.01 M) and borate buffer (pH = 10.5; 0.05 M). To ensure the stability and efficiency of the reaction, the presence of different nucleophilic reagents, namely (a) 2-mercaptoethanol (2-ME), (b) N-acetylcysteine (NAC), (c) tiopronin (Thiola), (d) 3-mercaptopropionic acid (3-MPA) and (e) captopril, was investigated. The method was validated (R2 = 0.9999, intra-day repeatability %RSD < 3.22%, inter-day precision %RSD = 1.83%, limits of detection 5.75 ng/mL and limits of quantification 17.43 ng/mL, recovery of five different concentrations 99.75-101.58%) and successfully applied to investigate the in vitro permeability of homotaurine using Franz diffusion cells. The apparent permeability (Papp) of HOM was compared with that of memantine, which is considered a potential therapeutic drug for various CNSs. Our study demonstrates that homotaurine exhibits superior permeability through the simulated blood-brain barrier compared to memantine, offering promising insights for enhanced drug delivery strategies targeting neurological conditions.

Smartphone-Based High-Throughput Fluorimetric Assay for Histidine Quantification in Human Urine Using 96-Well Plates.

A high-throughput fluorimetric assay for histidine was developed, using a 96-well plates platform. The analyte reacts selectively with o-phthalaldehyde under mild alkaline conditions to form a stable derivative. Instrumental-free detection was carried out using a smartphone after illumination under UV light (365 nm). The method was proved to be linear up to 100 µM histidine, with an LLOQ (lower limit of quantification) of 10 µM. The assay was only prone to interference from glutathione and histamine that exist in the urine samples at levels that are orders of magnitude lower compared to histidine. Human urine samples were analyzed following minimum treatment and were found to contain histidine in the range of 280 to 1540 µM. The results were in good agreement with an HPLC corroborative method.

Determination of o-phthalaldehyde for dose verification of the clinical disinfectant by fluorescent sequential injection analysis.

A new automated, generic analytical approach for determining the clinical disinfectant o-phthalaldehyde (OPA) is reported in this study. The proposed sequential injection analysis (SIA) is based on the online reaction of the OPA with glycine/N-acetylcysteine (NAC) in a neutral medium (pH = 7.0) to form a highly fluorescent isoindole derivative. All critical flow and reaction variables were investigated, while validation was carried out in the linearity detection range (0.0075-0.02%). As a result, excellent linearity (R2 > 0.99) and precision (1.5-2.4% for repeatability and 0.7-2.2% for reproducibility) were achieved for the reference OPA solutions. Furthermore, reasonable concentration verification of OPA disinfection (0.2-0.6%) in healthcare institutes can be achieved using the developed fluorescent SIA due to its good sensitivity (0.111 V/%) and precision (1.0-2.3% for intermediate precision) around the minimum effective concentration (MEC) of 0.3% for Cidex-OPA disinfectant.

Injectable antibacterial tissue-adhesive hydrogel based on biocompatible o-phthalaldehyde/amine crosslinking for efficient treatment of infected wounds.

Injectable antibacterial hydrogels have attracted considerable attention in wound management. However, the development of injectable hydrogels with excellent antibacterial activity, good biocompatibility, and strong tissue adhesion remains a challenge. In this study, an antibacterial tissue-adhesive hydrogel was developed based on a catalyst-free o-phthalaldehyde (OPA)/amine reaction by simply mixing OPA-terminated four-arm poly(ethylene glycol) (4aPEG-OPA) and ε-poly-l-lysine (ε-PLL) solutions. The hydrogel showed tunable gelation time, storage moduli, and degradation rate depending on the polymer concentration and 4aPEG-OPA/ε-PLL mass ratio. The hydrogel exhibited nearly 100% bacterial inhibition rates in-vitro against Gram-negative E. coli and Gram-positive S. aureus, while maintaining good biocompatibility. The hydrogel matched well in shape and tightly adhered to the tissue after in-situ formation at the wound sites. Following the treatment of rat models of full-thickness skin incisions and round wounds, the hydrogel effectively closed the wounds and promoted wound healing. Moreover, after administering to S. aureus infected full-thickness skin wounds, the hydrogel exhibited remarkable efficacy in inhibiting wound infection with a bacterial inhibition rate over 99.94%, achieving a significantly accelerated wound healing compared with the commercially available Prontosan® gel. Therefore, the hydrogel exhibits great potential as a wound dressing for infection prevention and promotion of healing.

The Effectiveness of Ultraviolet Smart D60 in Reducing Contamination of Flexible Fiberoptic Laryngoscopes.

OBJECTIVE: To compare the effectiveness of disinfection protocols utilizing a ultraviolet (UV) Smart D60 light system with Impelux™ technology with a standard Cidex ortho-phthalaldehyde (OPA) disinfection protocol for cleaning flexible fiberoptic laryngoscopes (FFLs). METHODS: Two hundred FFLs were tested for bacterial contamination after routine use, and another 200 FFLs were tested after disinfection with one of four methods: enzymatic detergent plus Cidex OPA (standard), enzymatic detergent plus UV Smart D60, microfiber cloth plus UV Smart D60, and nonsterile wipe plus UV Smart D60. Pre- and post-disinfection microbial burden levels and positive culture rates were compared using Kruskal-Wallis ANOVA and Fisher's two-sided exact, respectively. RESULTS: After routine use, approximately 56% (112/200) of FFLs were contaminated, with an average contamination level of 9,973.7 ± 70,136.3 CFU/mL. The standard reprocessing method showed no positive cultures. The enzymatic plus UV, microfiber plus UV, and nonsterile wipe plus UV methods yielded contamination rates of 4% (2/50), 6% (3/50), and 12% (6/50), respectively, with no significant differences among the treatment groups (p > 0.05). The pre-disinfection microbial burden levels decreased significantly after each disinfection technique (p < 0.001). The average microbial burden recovered after enzymatic plus UV, microfiber plus UV, and nonsterile wipe plus UV were 0.40 CFU/mL ± 2, 0.60 CFU/mL ± 2.4, and 12.2 CFU/mL ± 69.5, respectively, with no significant difference among the treatment groups (p > 0.05). Micrococcus species (53.8%) were most frequently isolated, and no high-concern organisms were recovered. CONCLUSION: Disinfection protocols utilizing UV Smart D60 were as effective as the standard chemical disinfection protocol using Cidex OPA. LEVEL OF EVIDENCE: NA Laryngoscope, 133:3512-3519, 2023.

An approach to quantify ortho-phthalaldehyde contamination on work surfaces.

Ortho-phthalaldehyde (OPA) is used as a high-level disinfectant for reusable medical devices in healthcare settings. The ACGIH recently adopted a Threshold Limit Value-Surface Limit (TLV-SL; 25 µg/100 cm2) for OPA surface contamination to prevent induction of dermal and respiratory sensitization following dermal exposure. However, there is no current validated method to measure OPA surface contamination. This study aimed to develop a standardized approach for sample collection and quantitative determination of OPA from work surfaces for use in risk assessment practices. The reported method utilises readily available commercial wipes to collect surface samples coupled with direct detection of OPA via liquid chromatography time of flight mass spectrometry (LC-ToF-MS). This approach avoided complex derivatization steps commonly required for the analysis of aldehydes. Method evaluation was conducted in accordance with the Occupational Safety and Health Administration (OSHA) surface sampling guidelines. Overall recoveries of 25 µg/100 cm2 of OPA from stainless steel and glass surfaces were 70% and 72%, respectively. The reported LOD for this method was 1.1 µg/sample and the LOQ was 3.7 µg/sample. OPA remained stable on the sampling medium for up to 10 days, when stored at 4 °C. The method was demonstrated in a workplace surface assessment at a local hospital sterilising unit, successfully detecting OPA on work surfaces. This method is intended to supplement airborne exposure assessment and provide a quantitative assessment tool for potential dermal exposure. When used in conjunction with a thorough occupational hygiene program that includes hazard communication, engineering controls, and personal protective equipment, skin exposure and consequent sensitization risks in the workplace can be minimized.

Naphthalene-2,3-dicarboxaldehyde as a pulsed-post column derivatization reagent; comparison with two alternative o-phthalaldehyde based chemistries for the determination of histamine.

In the present study, naphthalene-2,3-dicarboxaldehyde (NDA) was used in on-line post column derivatization (PCD) coupled to liquid chromatography under the new concept of Pulsed-PCD. In Pulsed-PCD, the reagents are introduced into the flowing stream of the mobile phase under precise timing overlapping the eluted analyte. The consumption of the reagents is minimized to a few microliters, resulting in a significant advantage, that is the use of expensive reagents in PCD. For this reason, NDA-CN chemistry was used for the determination of histamine in food samples, such as eggplant and spinach. Two additional methods were developed based on the reaction of histamine with o-phthalaldehyde (OPA), namely the classic OPA - nucleophilic compound reaction and the specific OPA - histamine reaction in alkaline medium. The chromatographic conditions and the Pulsed-PCD conditions were investigated, while the analytical figures of merit were satisfactory. In all three methods, a pulse of 50 µL was used (OPA/NDA + Buffer), reducing dramatically the consumption of PCD reagents.

Efficacy of high-level disinfection of endoscopes contaminated with Streptococcus equi subspecies equi with 2 different disinfectants.

BACKGROUND: Prevention of spread of Streptococcus equi subspecies equi (S. equi) after an outbreak is best accomplished by endoscopic lavage of the guttural pouch, with samples tested by culture and real time, quantitative polymerase chain reaction (qPCR). Disinfection of endoscopes must eliminate bacteria and DNA to avoid false diagnosis of carrier horses of S. equi. HYPOTHESIS/OBJECTIVES: Compare failure rates of disinfection of endoscopes contaminated with S. equi using 2 disinfectants (accelerated hydrogen peroxide [AHP] or ortho-phthalaldehyde [OPA]). The null hypothesis was that there would be no difference between the AHP and OPA products (based on culture and qPCR results) after disinfection. METHODS: Endoscopes contaminated with S. equi were disinfected using AHP, OPA or water (control). Samples were collected before and after disinfection and submitted for detection of S. equi by culture and qPCR. Using a multivariable logistic regression model-adjusted probability, with endoscope and day as controlled variables, the probability of an endoscope being qPCR-positive was determined. RESULTS: After disinfection, all endoscopes were culture-negative (0%). However, the raw unadjusted qPCR data were positive for 33% AHP, 73% OPA, and 71% control samples. The model-adjusted probability of being qPCR-positive after AHP disinfection was lower (0.31; 95% confidence interval [CI], -0.03-0.64) compared to OPA (0.81; 95% CI, 0.55-1.06), and control (0.72; 95% CI, 0.41-1.04). CONCLUSION AND CLINICAL IMPORTANCE: Disinfection using the AHP product resulted in significantly lower probability of endoscopes being qPCR-positive compared to the OPA product and control.

An Electrochemical o-Phthalaldehyde Sensor Using a Modified Disposable Screen-Printed Electrode with Polyacrylate Hydrogel for Concentration Verification of Clinical Disinfectant.

The study proposes an o-phthalaldehyde (OPA) sensor for rapid and reliable detection of OPA in healthcare disinfection practices, based on a hydrogel-modified screen-printed carbon electrode strip. The hydrogel film, which contains glycine and N-acetylcysteine, reacts with OPA to produce a reductive isoindole derivative. The derivative is then oxidized for OPA determination using cyclic voltammetry. The proposed sensor achieves an optimal detection time of 20-30 s and requires only a small analyte volume of 5 µL. It exhibits good precision (10%) and sensitivity (3.3 µA/cm2 mM) in a phosphate-buffered solution (pH 7.6), with excellent linearity (R2 > 0.97) and precision (<3%) in the detection range (0.2-0.6%) required for clinical OPA solutions. Moreover, the sensor demonstrates good concentration verification of Cidex-OPA disinfection in healthcare institutes, with high sensitivity (18.28 µA/cm2 mM) and precision around the minimum effective concentration (0.3%). Overall, the proposed sensor offers a promising and practical solution for accurate and reliable OPA detection in clinical disinfection practices.

A new application of isoindole fluorophore derivative in sitagliptin antidiabetic medication assay: Application to dosage forms and biological fluid evaluation.

Dipeptidyl peptidase-4 enzyme suppressant is a unique category of oral antidiabetic medication. Sitagliptin (STG) is a perfect member of this category and is pharmaceutically marketed alone or in combination with metformin. Here, the ideal application of an isoindole derivative for STG assay was developed using a feasible, easy-to-use, economic, and affordable method. STG as an amino group donor can form a luminescent derivative: isoindole on interaction with o-phthalaldehyde and the existence of (2-mercaptoethanol) 0.02% (v/v) as a thiol group donor. Excitation (339.7 nm) and emission (434.6 nm) wavelengths were used to monitor the isoindole fluorophore yield; moreover, each experimental variable was carefully investigated and adjusted. The calibration graph was constructed by plotting fluorescence intensities against STG concentrations, and controlled linearity was observed at concentrations ranging from 50 to 1000 ng/ml. The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines were analyzed in depth to prove the technique validation. The implementation of the present technique was extended successfully to the evaluation of various types of STG dose forms and spiking samples of human plasma and urine. The developed technique was shown to be an effective, simple, and quick replacement for quality control and clinical study evaluation of STG.

An integrative analytical approach designed for feasible tranexamic acid assay using o-phthalaldehyde as a fluorogenic probe: applications to tablets, ampoules, and urine.

Antifibrinolytic tranexamic acid (TRX) suppresses plasminogen activation to plasmin in a competitive way. TRX is approved for the management of heavy menstrual periods, hereditary angioedema, hemophilia, postpartum hemorrhage, surgery, tooth extraction, and severe blood loss after acute trauma. Here, the practical use of an isoindole derivative was established for a novel, easy-to-use, and affordable TRX assay. In the presence of a molecule containing a sulfhydryl group (2-mercaptoethanol) 0.02% v/v, the primary amine moiety in TRX allows its combination with o-phthalaldehyde to produce a luminous product. Excitation (338.8 nm) and emission (433.9 nm) wavelengths were used to monitor the isoindole fluorophore yield, and each operational variable was carefully examined and adjusted. The calibration graph was constructed with fluorescence intensity versus TRX concentration, excellent linearity was observed at concentrations between 40 and 950 ng/ml, and limit of detection and limit of quantitation were 41.3 and 13.6 ng/ml, respectively. The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines were used to validate the method. The developed method for TRX assay in various dosage forms and urine was successfully implemented and was shown to be an effective, simple, and quick replacement for the TRX assay in clinical trials and quality control.

Development and evaluation of pulsed - Post column derivatization in liquid chromatography as a concept to minimize reagent consumption.

In the current article, we propose an alternative approach to reduce the consumption of the reagents in liquid chromatography coupled to on-line post column derivatization. In our proposal post column reagents do not flow continuously but they are instead introduced as well-defined pulses (at microliter levels) that are merged on-line with the eluted analytes through precise tuning (Pulsed-Post Column Derivatization, Pulsed-PCD). The profiles of the pulses in terms of time and flow rate were investigated "visually" using caffeine as model compound (at 274 nm). The robustness of the procedure was evaluated by Monte Carlo simulations and was verified taking into account the precisions of typically used propulsion systems. As a proof of concept, we selected the determination of histidine in human urine after separation by cation exchange chromatography and Pulsed-PCD derivatization with o-phthalaldehyde. The consumption of the derivatizing reagent was downscaled to the microliter level per run, while the analytical results were within the expected ranges (110 - 1520 µmol L-1) and with good agreement with the corroborative method based on classic HPLC-PCD.

Coupling of Physical and Chromatographic Separation for Analyzing Cream Containing Miconazole, Mometasone Furoate and Gentamicin Sulphate.

High-performance liquid chromatographic method was developed, validated and applied for miconazole, mometasone and gentamicin in Momenta® cream. Physical separation was applied using two extraction procedures due to different solubility of the three components. First, a methanolic extract of the cream contained miconazole and mometasone was chromatographed on ODS-3 Inertsil C18 column (150 × 4.6, 5 µm) using acetonitrile: water (80:20, v/v) as a mobile phase, flow rate 1.5 mL·min-1, scanned at 230 nm, showing tR 2.817 and 6.808 min for mometasone and miconazole, respectively. Second, an aqueous extract of the cream containing gentamicin was derivatized with o-phthalaldehyde in order to enhance the gentamicin UV detection and subjected to ion pairing chromatography on Inertsil ODS-3 C18 column (150 × 4.6, 5 µm), using methanol: 0.025 M heptane sulphonic acid: glacial acetic acid (75:20:5, by volume) as a mobile phase, flow rate 0.8 mL·min-1, scanned at 330 nm where the three active gentamicin isomers were separated at tR 11.7, 15.6 and 18.3 min. Suitability of this method for quantitative estimation of the drugs was proved by validation according to ICH guidelines. The method was selective, precise and accurate so could be used for analysis of cream formulation in QC labs.

A photoluminescence sensor for in-situ monitoring of the dopamine neurotransmitters released from PC12 cells.

Constructing simple, stable, fast, and sensitive neurotransmitter-based sensors is a promising tool to diagnose neurological diseases. Dopamine (DA), "a catecholamine neurotransmitter" is important in transmitting nerve impulses. Therefore, great attention is taken to monitor DA concentrations received. The challenge in developing a DA-based sensor is to enhance its stability and sensitivity. Thus, we have used o-phthalaldehyde (OPA)/2-mercapto ethanol (2ME)/mesoporous silica instated of 2ME in solution. Here we have successfully developed a fluorescence DA neurotransmitters sensor. The sensor was used for detecting a wide range of concentrations of DA (5 nM to 5 µM). Effects of pH (4.3-11.4) and temperatures (25-70 °C) on the sensor efficiency were investigated. The detection limit was 1.35 × 10-11 mol/dm3, which is lower than the normal DA level in the central nervous system. The results indicated that using OPA/2ME/MSNPs has long-time stability over a year of its preparation. Moreover, the developed sensor showed high specificity towards DA in the presence of different interferences such as ascorbic acid or another catecholamine neurotransmitter such as γ-aminobutyric acid. Finally, the fabricated biosensor was used to monitor the DA neurotransmitter released from PC12 cells. Hence, it was successfully developed a simple and stable probe for accurate photoluminescence detection of DA neurotransmitters.

Bioconjugation via Hetero-Selective Clamping of Two Different Amines with ortho-Phthalaldehyde.

Amino groups are common in both natural and synthetic compounds and offer a very attractive class of endogenous handles for bioconjugation. However, the ability to differentiate two types of amino groups and join them with high hetero-selectivity and efficiency in a complex setting remains elusive. Herein, we report a new method for bioconjugation via one-pot chemoselective clamping of two different amine nucleophiles using a simple ortho-phthalaldehyde (OPA) reagent. Various α-amino acids, aryl amines, and secondary amines can be crosslinked to the ϵ-amino side chain of lysine on peptides or proteins with high efficiency and hetero-selectivity. This method offers a simple and powerful means to crosslink small molecule drugs, imaging probes, peptides, proteins, carbohydrates, and even virus particles without any pre-functionalization.

O-phthalaldehyde assisted surface enhanced Raman spectroscopy selective determination of trace homocysteine in serum.

High plasma homocysteine (Hcy) levels may indicate cardiovascular disease. However, sensitive and selective determination of Hcy remains a major challenge. Herein, we present a sensing strategy for Hcy by surface enhanced Raman scattering (SERS) method along with a specific reaction of o-phthalaldehyde (OPA) and Hcy. The obtained adduct 2-(1-carboxyl-3-thiopropyl)-1-isoindolinone (Hcy-OPA) can be directly detected by SERS using gold nanoparticles (Au NPs) as the substrate. The developed SERS method displays superior sensitivity (low detection limit of 2.50 × 10-12 mol L-1) with a broad linear range (5.00 × 10-10 -5.00 × 10-6 mol L-1). As a proof of real application, it can be used to detect Hcy in bovine serum samples with a concentration as low as 5.00 × 10-9 mol L-1, which is free from the interference of the other amino acids and glutathione.