Citrate-capped Gold Nanoparticles Research Articles

Alpha-Synuclein Aggregation Mechanism in the Presence of Nanomaterials.

Parkinson's disease (PD) is characterized by the toxic oligomeric and fibrillar phases formed by monomeric alpha-synuclein (α-syn). Certain nanoparticles have been demonstrated to promote protein aggregation, while other nanomaterials have been found to prevent the process. In the current work, we use nuclear magnetic resonance spectroscopy in conjunction with isothermal titration calorimetry to investigate the cause and mechanism of these opposing effects at the amino acid protein level. The interaction of α-syn with two types of nanomaterials was considered: citrate-capped gold nanoparticles (AuNPs) and graphene oxide (GO). In the presence of AuNPs, α-syn aggregation is accelerated, whereas in the presence of GO, aggregation is prevented. The study indicates that GO sequesters the NAC region of α-syn monomers through electrostatic and hydrophobic interactions, leading to a reduced elongation rate, and AuNPs leave the NAC region exposed while binding the N-terminus, leading to higher aggregation. The protein's inclination toward quicker aggregation is explained by the binding of the N-terminus of α-syn with the gold nanoparticles. Conversely, a comparatively stronger interaction with GO causes the nucleation and growth phases to be postponed and inhibits intermolecular interactions. Our finding offers novel experimental insights at the residue level regarding the aggregation of α-syn in the presence of various nanomaterials and creates new opportunities for the development of suitably functionalized nanomaterial-based therapeutic reagents against Parkinson's and other neurodegenerative diseases.

Coumarin Derivative and Gold Nanoparticle Conjugate as a Selective Fluorescent Sensor for Mercury Ion in Real Sample.

A biphenyl based coumarin fluorescent molecule, N,N'-bis(7-diethylamino-2-oxo-2H-chromen-3-yl)methylene)biphenyl-2-2'-dicarbohydrazide (molecule 1) has been synthesized and characterised. Photophysical studies of 1 exhibit solvent polarity dependent absorption and emission maxima. Citrate capped gold nanoparticles (AuNPs) have been mixed with molecule 1 for the preparation of AuNPs/1 conjugate. The association constant of the AuNPs/1 conjugate has been calculated to 4.54 × 104 M- 1. The AuNPs/1 conjugate has been found to detect Hg2+ ion selectively by fluorescence enhancement. While addition of molecule 1 into the solution of AuNPs, fluorescence intensity of 1 quenched. On addition of several monovalent, divalent and trivalent metal ion into the solution of AuNPs/1 conjugate separately, there was no change in fluorescence intensity of 1 has been observed. However, upon addition of Hg2+ ion into the solution of AuNPs/1 conjugate, the fluorescence intensity enhancement occurred, indicating released of 1 from the surface of AuNPs and probably aggregation of AuNPs took place in presence of Hg2+ ion. The AuNPs/1 conjugate has been found to have a detection limit of 2.3 × 10- 9 M for Hg2+ ion in aqueous solvent. Meanwhile, the AuNPs/1 conjugate have also been successfully applied for the determination of Hg2+ in real water samples.

Colorimetric Sensor Array for Simultaneous Assay of Catecholamine Neurotransmitters Using Various-Sized Citrate-Capped Gold Nanoparticles

Driven by the need to in situ monitoring of the endogenous substances in biological matrices, a simple, rapid and sensitive optical nanoarray system has been designed for determination and visual discrimination of four important catecholamine neurotransmitters: dopamine (DA), epinephrine (EP), norepinephrine (NE) and levodopa (LD). To fabricate this platform, spherical citrate-capped gold nanoparticles (AuNPs) in the size range of 13–42 nm have been employed as sensing elements. For each catecholamine different responses toward the AuNPs was obtained indicating unique aggregation kinetics. When the sensor array exposed to different catecholamines (CAs), both the color and UV–Vis absorbance spectra changed due to the interaction of analytes and AuNPs, creating a unique fingerprint-like pattern for each analyte which can be visually detected by naked eye. To analyze response profiles, we employed unsupervised chemometric algorithms including hierarchical cluster analysis (HCA) and principal component analysis (PCA) and satisfactory class separations were achieved. Furthermore, the sensitive RGB based color difference patterns were generated providing easily monitored visual output. Based on this sensor array, the set of four catecholamine neurotransmitters have been correctly identified and classified in the spiked real urine samples. The target analytes have been well distinguished at low concentrations of 0.3 − 4 μM DA, 0.8 − 10 μM EP, 0.8 − 8 μM NE, and 0.3 − 10 μM LD using the proposed “chemical nose” strategy. We believe that the established optical sensor array can be potentially employed as an efficient discrimination tool for diagnostic and therapeutic applications in the future.

Comparing silver and gold nanoislands’ surface plasmon resonance for bisacodyl and its metabolite quantification in human plasma

Gold and silver nanoparticles have witnessed increased scientific interest due to their colourful colloidal solutions and exceptional applications. Comparing the localized surface plasmon resonance (LSPR) of gold and silver nanoparticles is crucial for understanding and optimizing their optical properties. This comparison informs the design of highly sensitive plasmonic sensors, aids in selecting the most suitable nanoparticles for applications like surface-enhanced infrared spectroscopy (SEIRA) and biomedical imaging, and guides the choice between gold and silver nanoparticles based on their catalytic and photothermal properties. Ultimately, the study of LSPR facilitates the tailored use of these nanoparticles in diverse scientific and technological applications. Two SEIRA methods combined with partial least squares regression (PLSR) chemometric tools were developed. This development is based on the synthesis of homogeneous, high-dense deposited metal nanoparticle islands over the surface of glass substrates to be used as lab-on-chip SEIRA sensors for the determination of bisacodyl (BIS) and its active metabolite in plasma. SEM micrographs revealed the formation of metallic islands of colloidal citrate-capped gold and silver nanoparticles of average sizes of 29.7 and 15 nm, respectively. BIS and its active metabolite were placed on the nanoparticles’ coated substrates to be directly measured, then PLSR chemometric modelling was used for the quantitative determinations. Plasmonic citrate-capped gold nanoparticle substrates showed better performance than those prepared using citrate-capped silver nanoparticles in terms of preparation time, enhancement factor, PLSR model prediction, and quantitative results. This study offers a way to determine BIS and its active metabolite in the concentration range 15–240 ng/mL in human plasma using inexpensive disposable glass-coated substrates that can be prepared in 1 h to get results in seconds with good recovery between 98.77 and 100.64%. The sensors provided fast, simple, selective, molecular-specific and inexpensive procedures to determine molecules in their pure form and biological fluid.

Exploring alkyl-diamine chain length effects on electrochemical behavior of AuNPs fabricated electrodes: Influence of linkers on the sensitive detection of hydrazine

In this electrochemical exploration, we scrutinized the influence of alkyl-diamine (AD) chain length as crucial linkers between glassy carbon electrodes (GCE) and citrate-capped gold nanoparticles (Cit-AuNPs), focusing on their conductive behavior and sensing proficiency, particularly in hydrazine detection. Meticulous examination of self-assembled monolayers (SAMs) formed by three distinct ADs, namely 1,6-hexanediamine (HDA), 1,8-octanediamine (ODA) and 1,10-decanediamine (DDA) unfolded over GC surfaces revealed a precise adherence to Langmuir adsorption kinetics during the SAM formation process. Utilizing cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the electrochemical activity of the [Ru(NH₃)₆]³⁺/²⁺ redox pair at electrodes modified with ADs was investigated. The proposed mechanism involves a Michael-like nucleophilic addition process at the GC surface/diamine solution interface during the SAM formation. Analysis across various techniques underscored the compact nature of the DDA-formed SAM in comparison to HDA and ODA. Exploiting the free amine functional groups on the SAMs, the as-synthesized Cit-AuNPs were attached on the electrode surface and investigated comprehensively through CV, EIS, attenuated total reflection Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Remarkably, Cit-AuNPs attached DDA-SAM/GC electrode offered superior electro active surface area, establishing an advanced electrochemical platform for carcinogenic hydrazine determination. The DDA/Cit-AuNPs electrode demonstrated a linear determination range of 0.003–1 mM, limits of detection at 11 nM, and sensitivity of 1080 µA mM−1 cm−2. This study gives a complete picture of how AD chain lengths, SAM formation, Cit-AuNPs attachment, and electrocatalytic performance work together to make an advanced electrochemical sensing scaffold for environmental pollutants determination.

Protein-Functionalized Gold Nanospheres with Tunable Photothermal Efficiency for the Near-Infrared Photothermal Ablation of Biofilms.

Temperature-responsive nanostructures with high antimicrobial efficacy are attractive for therapeutic applications against multidrug-resistant bacteria. Here, we report temperature-responsive nanospheres (TRNs) engineered to undergo self-association and agglomeration above a tunable transition temperature (Tt). The temperature-responsive behavior of the nanoparticles is obtained by functionalizing citrate-capped spherical gold nanoparticles (AuNPs) with elastin-like polypeptides (ELPs). Using protein design principles, we achieve a broad range of attainable Tt values and photothermal conversion efficiencies (η). Two approaches were used to adjust this range: First, by altering the position of the cysteine residue used to attach ELP to the AuNP, we attained a Tt range from 34 to 42 °C. Then, by functionalizing the AuNP with an additional small globular protein, we could extend this range to 34-50 °C. Under near-infrared (NIR) light exposure, all TRNs exhibited reversible agglomeration. Moreover, they showed an enhanced photothermal conversion efficiency in their agglomerated state relative to the dispersed state. Despite their spherical shape, TRNs have a photothermal conversion efficiency approaching that of gold nanorods (η = 68 ± 6%), yet unlike nanorods, the synthesis of TRNs requires no cytotoxic compounds. Finally, we tested TRNs for the photothermal ablation of biofilms. Above Tt, NIR irradiation of TRNs resulted in a 10,000-fold improvement in killing efficiency compared to untreated controls (p < 0.0001). Below Tt, no enhanced antibiofilm effect was observed. In conclusion, engineering the interactions between proteins and nanoparticles enables the tunable control of TRNs, resulting in a novel antibiofilm nanomaterial with low cytotoxicity.

Selection and characterization of ssDNA aptamer targeting Macrobrachium rosenbergii nodavirus capsid protein: A potential capture agent in gold-nanoparticle-based aptasensor for viral protein detection.

The giant freshwater prawn holds a significant position as a valuable crustacean species cultivated in the aquaculture industry, particularly well-known and demanded among the Southeast Asian countries. Aquaculture production of this species has been impacted by Macrobrachium rosenbergii nodavirus (MrNV) infection, which particularly affects the larvae and post-larvae stages of the prawn. The infection has been recorded to cause mortality rates of up to 100% among the affected prawns. A simple, fast, and easy to deploy on-site detection or diagnostic method is crucial for early detection of MrNV to control the disease outbreak. In the present study, novel single-stranded DNA aptamers targeting the MrNV capsid protein were identified using the systematic evolution of ligands by exponential enrichment (SELEX) approach. The aptamer was then conjugated with the citrate-capped gold nanoparticles (AuNPs), and the sensitivity of this AuNP-based aptasensor for the detection of MrNV capsid protein was evaluated. Findings revealed that the aptamer candidate, APT-MrNV-CP-1 was enriched throughout the SELEX cycle 4, 9, and 12 with the sequence percentage of 1.76%, 9.09%, and 12.42%, respectively. The conjugation of APT-MrNV-CP-1 with citrate-capped AuNPs exhibited the highest sensitivity in detecting the MrNV capsid protein, where the presence of 62.5 nM of the viral capsid protein led to a significant agglomeration of the AuNPs. This study demonstrated the practicality of an AuNP-based aptasensor for disease diagnosis, particularly for detecting MrNV infection in giant freshwater prawns.

Unusual gold nanoparticle-antibody interactions

The formation of an antibody (Ab) protein corona surrounding gold nanoparticles (AuNPs) is a crucial step in the design of immunological assays. The Ab corona stabilizes AuNPs, preventing their aggregation even at high ionic strength, and can be achieved by simply mixing Abs and AuNPs. In this paper, we report the unusual interactions between AuNPs and the antibody against L1 Cell Adhesion Molecule (L1CAM) purified from rabbits. We have observed that at low ionic strength, the addition of a wide range of concentrations of rabbit monoclonal Abs against L1CAM protein immediately causes the coagulation of citrate-capped gold nanoparticles. This finding is surprising since the addition of proteins to colloidal gold usually forms a stable protein corona. The combination of extinction spectra, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements reveals the presence of small clusters of AuNPs coated by the antibodies, as well as micron-sized antibody aggregates. Furthermore, static light scattering measurements demonstrate that Ab self-interactions are attractive (with a negative second virial coefficient, B2) and induce very slow Ab self-aggregation over several months. Overall, these results indicate that, at low ionic strength, the presence of AuNPs enhances Ab-Ab interactions, leading to their rapid aggregation. Simultaneously, the self-aggregation of the antibodies coating the AuNPs results in the formation of nanoparticle clusters. The addition of NaCl to increase the ionic strength fully reverses the coagulation of AuNPs (the Ab-coated AuNPs repel each other) and dissolves the Ab aggregates (the Ab interactions become repulsive, with a positive B2). The AuNPs-induced enhancement of the aggregation process can be explained by considering that the highly favorable binding of Abs on the gold surface compensates for the entropic penalty associated with Ab-Ab aggregation. The phenomenon we observed is specific to anti-L1CAM purified from rabbits and aligns with very old reports on AuNP coagulation induced specifically by the immunoglobulins present in the cerebrospinal fluid of patients suffering from neurosyphilis or multiple sclerosis (C. Lange Zeitschr. Chemotherap., 1912, 1, 44). It is reasonable to hypothesize that other antibodies exhibit this unusual behavior, so this work may aid in the interpretation of “anomalous” results that might otherwise be attributed to errors in fine-tuning AuNPs-Abs conjugation protocols.

On the interaction and nanoplasmonics of gold nanoparticles and lipoproteins

The extracellular space is nanostructured, populated by heterogeneous classes of nanoparticles, e.g., extracellular vesicles and lipoproteins, which “made by cells for cells'' mediate intercellular, inter-organ, cross-species, and cross-kingdom communication. However, while techniques to study ENP biology in-vitro and in-vivo are becoming available, knowledge of their colloidal and interfacial properties is poor, although much needed. This paper experimentally shows, for the first time, that the aggregation of citrate-capped gold nanoparticles (AuNPs) triggered by lipid vesicle membranes and the related characteristic redshift of the plasmonic signature also applies/extends to lipoproteins. Such interaction leads to the formation of AuNP-lipoprotein hybrid nanostructures and is sensitive to lipoprotein classes and AuNP/lipoprotein molar ratio, paving the way to further synthetic and analytical developments.

Synthesis and characterization of citrate-capped gold nanoparticles and their application in selective detection of creatinine (A kidney biomarker)

A simple, sensitive, and highly selective detection method was developed for creatinine using citrate-capped gold nanoparticles (C-AuNPs). TEM analysis confirmed the synthesis of the C-AuNPs and they were mostly spherical in shape. FTIR data showed peaks at 3302 cm−1, 1635 cm−1, 1219 cm−1 and 771 cm−1 indicating the presence of O–H, C=C, C–O, C–C groups on the surface of the synthesized C-AuNPs. XRD analysis revealed peaks at 33.8, 44.4, 64.6, 77.5, and 81.6° confirming the crystalline nature of the C-AuNPs. The principle of this method is based on the aggregation of C-AuNPs induced by the creatinine molecules which has been successfully employed for the colorimetric detection of creatinine ranging from 0.3 to 0.8 μg/100 μl (3–8 ppm). The degree of aggregation of C-AuNPs was found to have a linear relationship with the concentration of creatinine which allows the development of a colour gradient based on the varying creatinine concentrations. UV–Vis spectrophotometric analysis further confirmed the selectivity of the method among different analytes such as ascorbic acid, nicotinic acid, polyvinyl pyrrolidone, glucose, uric acid, and bovine serum albumin. It has also been successfully applied for the detection of creatinine in urine mimic samples with good recovery rates. Therefore, this method can be successfully employed for both qualitative and quantitative analysis of creatinine.

Effect of large ammonium cations on the aggregation kinetics of citrate capped gold nanoparticles

Effect of large ammonium cations on the aggregation kinetics of citrate capped gold nanoparticles

Study on the preparation of novel flavonol-gold nanoparticles antioxidants and the mechanism of protein corona formation

In this work, we reported the methodology involved in the binding of galangin/kaempferol/quercetin/myricetin onto the surface of 10.3 nm and 31.3 nm citrate-capped gold nanoparticles (AuNPs) by a simple in situ method to prepare the eight novel flavonol-AuNPs antioxidants. We systematically performed UV–vis spectroscopy, the hydrodynamic diameter, and zeta potential to characterize the novel flavonol-AuNPs antioxidants. The antioxidative effect of the novel flavonol-AuNPs antioxidants was determined using DPPH radical, hydroxyl radical and superoxide anion radical scavenging assays. The results indicate that the novel flavonol-AuNPs antioxidants scavenging ability of these three free radicals is significantly enhanced compared with flavonols or AuNPs. The scavenging capacity of 31.3 nm flavonol-AuNPs antioxidants is greater than that of 13.3 nm flavonol-AuNPs antioxidants. The free radical scavenging ability of quercetin/myricetin-AuNPs antioxidants is higher than that of galangin/kaempferol-AuNPs antioxidants. And then, the mechanism of protein corona formation between the eight novel AuNPs-flavonol antioxidants and γ-globulin/fibrinogen/trypsin/pepsin and the conformational changes of the four proteins caused by the protein corona formation were systematically and quantitatively investigated by various spectral techniques. Overall, we ascertain the fact that this kind of novel flavonol-AuNPs antioxidants will contribute to the development of safe and effective AuNPs antioxidants in biological systems.

Colorimetric recognition of fluoxetine and sertraline using citrate-capped gold nanoparticles

Colorimetric recognition of fluoxetine and sertraline using citrate-capped gold nanoparticles

LSPR-Based Aptasensor for Rapid Urinary Detection of NT-proBNP.

N-terminal pro-brain natriuretic peptide (NT-proBNP) is a myocardial stress biomarker that can be found in serum or plasma, saliva, and urine in the context of cardiovascular disease. In this study, we developed a rapid (~25 min) and straightforward localized surface plasmon resonance (LSPR)-based assay for detecting NT-proBNP in urine. The assay employs citrate-capped gold nanoparticles (AuNPs) and an aptamer specific for NT-proBNP, which initially interacts with NT-proBNP. The remaining unbound aptamer then interacts with the AuNPs, and the addition of NaCl induces the aggregation of the unprotected AuNPs, resulting in a decrease in absorbance at the LSPR band (A521) and an increase in absorbance at 750 nm (A750). The concentration of NT-proBNP showed a linear correlation with the aggregation ratio (A521/A750), and the assay demonstrated a limit of detection (LOD) of 0.303 µg·L-1 and a detection range of 0.566-8 µg·L-1. However, the presence of sulfur-containing proteins in saliva and fetal bovine serum hindered the detection of NT-proBNP in these biofluids. Nevertheless, the assay successfully detected NT-proBNP in diluted urine with an LOD of 0.417 µg·L-1 and a detection range of 0.589-6 µg·L-1. The observed values in urine samples from preterm infants with cardiovascular disease fell within this range, indicating the potential clinical relevance of the assay. The recovery percentages ranged from 92.3 to 116.3%. Overall, our findings suggest that the LSPR-based assay for NT-proBNP detection in urine can be a valuable tool for the diagnosis and treatment of cardiovascular disease.

Transient response to perturbations in flow synthesis of citrate capped gold nanoparticles

This work reports the transient behavior of continuous flow synthesis of gold nanoparticles (Au NPs) when subjected to perturbations in operating conditions using controlled experiments. The intricacies are captured through a detailed mathematical model. Reversed Turkevich protocol was used for synthesis of Au NPs. The synthesis was first studied in batch mode to investigate the reaction kinetics and reproducibility of the process. The optimal set of operating conditions viz., residence time, flow rate, temperature was then used for flow synthesis in a 2 m, 1/16″ Polytetrafluoroethylene (PTFE) reactor with micromixer. Reactor clogging was avoided by using segmented flow. Inline UV measurement was used for real time monitoring of the process. Transient experiments were performed by abruptly changing the operating conditions. A mathematical model was found to be accurate in predicting the transient behavior of the exit precursor concentration and the particle size for unsteady state synthesis. Even a small change in process variables for short duration was found to disturb the quality of Au NPs for a significantly longer duration. Of the three operating parameters, the effect of temperature variation was seen to have a prolonged effect where the system remained in unsteady state for long time.

Spectrophotometric and colorimetric trivalent chromium ions detection in aqueous solution based on citrate-capped gold nanoparticles

Spectrophotometric and colorimetric trivalent chromium ions detection in aqueous solution based on citrate-capped gold nanoparticles

MiRNA 143 based nanobiosensor to diagnose pancreatic cancer

This work exploits miRNA 143, a biomarker to detect pancreatic cancer. Recent reports from GLOBOCAN show that cases of pancreatic cancer will increase from 557,688 in 2025 to 815,276 by 2040. Furthermore, the 5-year survival rate of patients diagnosed with pancreatic cancer is only 14%, though it can be improved to 43% if diagnosed early. This necessitates the requirement for early diagnosis which will help in providing proper treatment. However, low concentration of tumor markers at early stage makes it difficult to diagnose. MicroRNAs (miRNAs) are considered an important tool for early diagnosis of cancer, since they appear as circulating markers in blood at early stage itself. In view of this, we have developed an electrochemical sensor to detect miRNA143. The self-assembled monolayers of cysteine hydrochloride were created on gold electrode surface followed by the immobilization of citrate-capped gold nanoparticles (10–25 nm). The amino-labeled single-stranded DNA probe against miRNA143 formed covalent bonding with citrate-capped gold nanoparticles. Non-specific binding to the platform was avoided by using gelatin as a blocking agent. Further, electrochemical measurements were recorded in response to target miRNA143. Characterization of fabricated miRNA143 gold printed electrode was done through cyclic voltammetry (CV). Cyclic voltammetric curve response recorded after addition of miRNA143 spiked FBS sample onto the fabricated electrode from 9.9ag/ml to 9.9 ng/ml (1.4aM to 1.4 nM), shows decreasing redox peak height with increasing concentration. Similar behavior was observed for saturation current through chronoamperometric analysis and differential pulse voltammetric measurements. The calibration plots of peak current response, saturation current with the increasing concentrations of miRNA143 were plotted. The sensitivity of the nanosensor as calculated from DPV, Chronoamperometry and CV measurements was 201.11 µA/g/ml/cm2, 125.98 µA/g/ml/cm2 and 95.55 µA/g/ml/cm2 and respectively with lower limit of detection (LLOD) of 1.4aM. LLOD of 1.4aM makes it a promising platform for sensing miRNA 143 and as a diagnostic tool for early diagnosis of pancreatic cancer.

Visual detection and highly sensitive quantification of antibiotic meropenem in pharmaceutical and human plasma samples using gold nanoparticles

ABSTRACT Meropenem is a broad-spectrum β-lactam antibiotic effective against a wide variety of gram-positive and gram-negative organisms, and has been extensively used in the intensive care unit (ICU) for severe infections caused by susceptible microorganisms that are resistant to other available drugs. A novel visual detection and highly sensitive method for meropenem quantification has been developed for the first time, based on the aggregation of citrate-capped gold nano particles (AuNPs) induced by the interaction with meropenem, leading to the change in surface plasmon resonance (SPR) properties of AuNPs. By naked eyes, one can detect meropenem trace by the visual change of gold solution color from red to blue, corresponding to the shift of absorbance maximum in the UV-Vis spectrum from 520 nm to 660 nm. Quantification of meropenem is possible through a linear relationship between the optical absorption ratio A660/A520 and the logarithm of meropenem concentrations. The present method has high recovery (97.6–101.5%), high precision (RSD<4.5%), and selectivity over other possible interferences such as glucose, sucrose, lactose, and sodium carbonate. This method has been successfully applied to determine meropenem in several pharmaceutical samples with a very low limit of detection (LOD) of 0.06 mg/L. Cross-checks with HPLC-DAD method show a good agreement between the two methods. For blood analysis, in combination with liquid-liquid extraction, the developed method presents high specificity, low LOD of 0.64 mg/L, and applicability to analysis of plasma samples taken from patients treated with meropenem under intensive care.

Cross-frontal mode: An alternative methodology for Taylor dispersion analysis of monomodal sample

Taylor dispersion analysis (TDA) is a technique dedicated to the determination of the molecular diffusion coefficient (D) of species, using band broadening of an analyte in a laminar flow. Two modes are commonly used to perform TDA: pulse and frontal modes. In each case, a fitting of the signal is required. We propose here a third mode denoted as cross-frontal mode, combining two crossed sample fronts without modification of a classical CE device for the rapid and accurate determination of D of caffeine, reduced glutathione (GSH), insulin from bovine pancreas, bovine serum albumin (BSA) and citrate-capped gold nanoparticles (AuNP). Theoretical aspects and methodology are described, showing a good correlation between the so-called cross-frontal mode and usual frontal mode. Limitations of the techniques are also assessed, and are similar to regular modes while no fitting is required. This new methodology allows improving the sensitivity toward low concentrated sample compared to pulse mode, and an alternative mathematical treatment compared to regular TDA modes.

Hyaluronic acid-magnetic fluorescent polydopamine/gold-based fluorescent probe for bioimaging of CD44 over-expressed cancer cells

CD44 is a transmembrane glycoprotein (P-glycoprotein) that expressed in a large scale on the surface membrane of breast cancer cells. The CD44 receptor has been employed for various medial aims such as imaging, drug delivery, and etc. In the present work, the surface of citrate-capped gold nanoparticles (cit-AuNPs) was modified with magnetic polydopamine nanoparticles to provide fluorescent nanocomposite and amine groups for attachment to hyaluronic acid (HA) molecules. HA molecules have been bonded to the surface of fluorescent polydopamine nanoparticles (FPNPs) via the formation of amide bonds between carboxyl (COOH) group of HA and amine groups of the FPNPs. Due to the presence of the HA molecules, the MNPs-FPNPs/AuNPs/HA can attach to the CD44-overexpressed MCF-7 cells with high specificity and could be employed for bioimaging aims. Fluorescence microscopy was applied for bioimaging of the MNPs-FPNPs/AuNPs/HA internalized cancer cells. Obtained results offered that the MNPs-FPNPs/AuNPs/HA can especially and efficiently internalize to the cells and differentiate CD44-positive cancer cells and normal cells of HFFF-2 cells. Also, the MNPs-FPNPs/AuNPs/HA has a biocompatible nature with the toxic levels around 250 μg/mL levels. As a conclusion, the MNPs-FPNPs/AuNPs/HA is a good candidate for specific bioimaging applications of CD44−overexpressed MCF-7 cancer cells with high physicochemical stability and advantageous spectral features.