Gold nanoparticles (AuNPs) are extensively studied nanoparticles (NPs) and are known to have profound applications in medicine. There are various methods to synthesize AuNPs which are generally categorized into two main types: chemical and physical synthesis. Continuous efforts have been devoted to search for other more environmental-friendly and economical large-scale methods, such as environmentally friendly biological methods known as green synthesis. Green synthesis is especially important to minimize the harmful chemical and toxic by-products during the conventional synthesis of AuNPs. Green materials such as plants, fungi, microorganisms, enzymes and biopolymers are currently used to synthesize various NPs. Biosynthesized AuNPs are generally safer for use in biomedical applications since they come from natural materials themselves. Multiple surface functionalities of AuNPs allow them to be more robust and flexible when combined with different biological assemblies or modifications for enhanced applications. This review focuses on recent developments of green synthesized AuNPs and discusses their numerous biomedical applications. Sources of green materials with successful examples and other key parameters that determine the functionalities of AuNPs are also discussed in this review.
The identification of rice bacterial leaf blight disease requires a simple, rapid, highly sensitive, and quantitative approach that can be applied as an early detection monitoring tool in rice health. This paper highlights the development of a turn-off fluorescence-based immunoassay for the early detection of Xanthomonas oryzae pv. oryzae (Xoo), a gram-negative bacterium that causes rice bacterial leaf blight disease. Antibodies against Xoo bacterial cells were produced as specific bio-recognition molecules and the conjugation of these antibodies with graphene quantum dots and gold nanoparticles was performed and characterized, respectively. The combination of both these bio-probes as a fluorescent donor and metal quencher led to changes in the fluorescence signal. The immunoreaction between AntiXoo-GQDs, Xoo cells, and AntiXoo-AuNPs in the immuno-aggregation complex led to the energy transfer in the turn-off fluorescence-based quenching system. The change in fluorescence intensity was proportional to the logarithm of Xoo cells in the range of 100-105 CFU mL-1. The limit of detection was achieved at 22 CFU mL-1 and the specificity test against other plant disease pathogens showed high specificity towards Xoo. The detection of Xoo in real plant samples was also performed in this study and demonstrated satisfactory results.
Cervical cancer is the third most common highest mortality in women worldwide. The use of standard chemotherapeutic drugs against cervical cancer patients received several side effects. Therefore, we focused phytoconsituents-mediated synthesis of gold nanoparticles (AuNPs) considered as greatest attention in the treatment of cervical cancer. In this present study, we reported that green synthesis of AuNPs by using with Alternanthera Sessilis aqueous extract. Synthesis of AuNPs were characterized by UV visible spectroscopy, energy dispersive X-ray (EDX), selected area diffraction pattern (SAED), Fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM) and atomic force microscope. Synthesized AuNPs confirmed by the UV absorption maximum at 535 and crystal structure of gold AuNPs was further confirmed by EDX and SAED. TEM and atomic force microscopy images show the size and morphological distribution of nanoparticles. FTIR analysis was confirmed the hydroxyl groups, amine and alkaline groups of biomolecules are present in the AuNPs. Moreover, AuNPs induce cytotoxicity in cervical cancer cells and also induce apoptosis through modulating intrinsic apoptotic mechanisms in cervical cancer cells. This green synthesis of AuNPs from Alternanthera sessilis approach was easy, large scaled up and eco-friendly.
With the long-term goal of developing an ultra-sensitive microcantilever-based biosensor for versatile biomarker detection, new controlled bioreceptor-analytes systems are being explored to overcome the disadvantages of conventional ones. Gold (Au) microwires have been used as a probe to overcome the tolerance problem that occurs in response to changes in environmental conditions. However, the cytotoxicity of Au microwires is still unclear. Here, we examined the cytotoxicity of Au microwires systems using both commercial and as-synthesised Au microwires. In vitro experiments show that commercial Au microwires with an average quoted length of 5.6 µm are highly toxic against Gram-negative Escherichia coli (E. coli) at 50 µg/mL. However, this toxicity is due to the presence of CTAB surfactant not by the microwires. Conversely, the as-synthesised Au microwires show non-cytotoxicity even at the maximum viable concentration (330 µg/mL). These findings may lead to the development of potentially life-saving cytotoxicity-free biosensors for an early diagnostic of potential diseases.
A new era of metal-based drugs started in the 1960s, heralded by the discovery of potent platinum-based complexes, commencing with cisplatin [(H₃N)₂PtCl₂], which are effective anti-cancer chemotherapeutic drugs. While clinical applications of gold-based drugs largely relate to the treatment of rheumatoid arthritis, attention has turned to the investigation of the efficacy of gold(I) and gold(III) compounds for anti-cancer applications. This review article provides an account of the latest research conducted during the last decade or so on the development of gold compounds and their potential activities against several cancers as well as a summary of possible mechanisms of action/biological targets. The promising activities and increasing knowledge of gold-based drug metabolism ensures that continued efforts will be made to develop gold-based anti-cancer agents.
The unique property of gold nanoparticles (Au NP) to induce colour change and the versatility of graphene oxides (GO) in surface modification makes them ideal in the application of colorimetric biosensor. Thus we developed a label free optical method to detect DNA hybridization through a visually observed colour change. The Au NP is conjugated to a DNA probe and is allowed to hybridize with the DNA target to the GO thus causing a change in colour from pinkish-red to purplish blue. Spectrophometry analysis gave a wavelength shift of 22 nm with 1 µM of DNA target. Sensitivity testing using serially diluted DNA conjugated GO showed that the optimum detection was at 63 nM of DNA target with the limit at 8 nM. This proves the possibility for the detection of DNA hybridization through the use of dual nanoparticle system by visual observation.
We have developed a colorimetric biosensor using a dual platform of gold nanoparticles and graphene oxide sheets for the detection of Salmonella enterica. The presence of the invA gene in S. enterica causes a change in color of the biosensor from its original pinkish-red to a light purplish solution. This occurs through the aggregation of the primary gold nanoparticles-conjugated DNA probe onto the surface of the secondary graphene oxide-conjugated DNA probe through DNA hybridization with the targeted DNA sequence. Spectrophotometry analysis showed a shift in wavelength from 525 nm to 600 nm with 1 μM of DNA target. Specificity testing revealed that the biosensor was able to detect various serovars of the S. enterica while no color change was observed with the other bacterial species. Sensitivity testing revealed the limit of detection was at 1 nM of DNA target. This proves the effectiveness of the biosensor in the detection of S. enterica through DNA hybridization.
To investigate the safety and efficacy of subretinal injection of human Wharton's Jelly-derived mesenchymal stem cells (hWJ-MSCs) on retinal structure and function in Royal College of Surgeons (RCS) rats.
Sonodynamic therapy (SDT) emerges as a promising non-invasive alternative for eradicating malignant tumours. However, its therapeutic efficacy remains limited due to the lack of sonosensitisers with high potency and biosafety. Previously, gold nanorods (AuNRs) have been extensively studied for their applications in photodynamic or photothermal cancer therapy, but their sonosensitising properties are largely unexplored. Here, we reported the applicability of alginate-coated AuNRs (AuNRsALG) with improved biocompatibility profiles as promising nanosonosensitisers for SDT for the first time. AuNRsALG were found stable under ultrasound irradiation (1.0 W/cm2, 5 min) and maintained structural integrity for 3 cycles of irradiation. The exposure of the AuNRsALG to ultrasound irradiation (1.0 W/cm2, 5 min) was shown to enhance the cavitation effect significantly and generate a 3 to 8-fold higher amount of singlet oxygen (1O2) than other reported commercial titanium dioxide nanosonosensitisers. AuNRsALG exerted dose-dependent sonotoxicity on human MDA-MB-231 breast cancer cells in vitro, with ∼ 81% cancer cell killing efficacy at a sub-nanomolar level (IC50 was 0.68 nM) predominantly through apoptosis. The protein expression analysis showed significant DNA damage and downregulation of anti-apoptotic Bcl-2, suggesting AuNRsALG induced cell death through the mitochondrial pathway. The addition of mannitol, a reactive oxygen species (ROS) scavenger, inhibited cancer-killing effect of AuNRsALG-mediated SDT, further verifying that the sonotoxicity of AuNRsALG is driven by the production of ROS. Overall, these results highlight the potential application of AuNRsALG as an effective nanosonosensitising agent in clinical settings.
Label-free-based detection is pivotal for real-time monitoring of biomolecular interactions and to eliminate the need for labeling with tags that can occupy important binding sites of biomolecules. One simplest form of label-free-based detection is ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy, which measure changes in reflectivity as a means to monitor immobilization and interaction of biomolecules with their corresponding partners. In biosensor development, the platform used for the biomolecular interaction should be suitable for different molecular recognition elements. In this study, gold (Au)-coated polycarbonate was used as a platform and as a proof-of-concept, erythropoietin (EPO), a doping substance widely abused by the athletes was used as the target. The interaction of EPO with its corresponding molecular recognition elements (anti-EPO monoclonal antibody and anti-EPO DNA aptamer) is monitored by UV-vis-NIR spectroscopy. Prior to this, to show that UV-vis-NIR spectroscopy is a suitable method for measuring biomolecular interaction, the interaction between biotin and streptavidin was demonstrated via this strategy and reflectivity of this interaction decreased by 25%. Subsequent to this, interaction of the EPO with anti-EPO monoclonal antibody and anti-EPO DNA aptamer resulted in the decrease of reflectivity by 5% and 10%, respectively. The results indicated that Au-coated polycarbonate could be an ideal biosensor platform for monitoring biomolecular interactions using UV-vis-NIR spectroscopy. A smaller version of the Au-coated polycarbonate substrates can be derived from the recent set-up, to be applied towards detecting EPO abuse among atheletes.
Several recent studies have reported that gold nanoparticles (AuNPs) attenuate hyperglycemia in diabetic animal models without any observed side effects. The present study was intended to provide insight into the effects of 50-nm AuNPs on diabetic kidney disease. Adult male rats were divided into three groups (n = 7/group): control (non-diabetic, ND), diabetic (D), and diabetic treated intraperitoneally with 50-nm AuNPs (AuNPs + D; 2.5 mg/kg/day) for 7 weeks. Diabetes was induced by a single-dose injection of 55 mg/kg streptozotocin. The result showed that AuNP treatment prevented diabetes-associated increases in the blood glucose level. Reduction in 24-h urinary albumin excretion rate, glomerular basement membrane thickness, foot process width, and renal oxidative stress markers was also demonstrated in the AuNP-treated group. In addition, the results showed downregulation effect of AuNPs in renal mRNA or protein expression of transforming growth factor β1 (TGF-β1), fibronectin, collagen IV, tumor necrosis factor-α (TNF-α), and vascular endothelial growth factor-A (VEGF-A). Moreover, the protein expression of nephrin and podocin, podocyte markers, in glomeruli was increased in the AuNPs + D group compared with the D group. These results provide evidence that 50-nm AuNPs can ameliorate renal damage in experimental models of diabetic nephropathy through improving the renal function and downregulating extracellular matrix protein accumulation, along with inhibiting renal oxidative stress and amelioration of podocyte injury.
Due to the low titer or uneven distribution of Citrus tristeza virus (CTV) in field samples, detection of CTV by using conventional detection techniques may be difficult. Therefore, in the present work, the cadmium-telluride quantum dots (QDs) was conjugated with a specific antibody against coat protein (CP) of CTV, and the CP were immobilized on the surface of gold nanoparticles (AuNPs) to develop a specific and sensitive fluorescence resonance energy transfer (FRET)-based nanobiosensor for detecting CTV. The maximum FRET efficiency for the developed nano-biosensor was observed at 60% in AuNPs-CP/QDs-Ab ratio of 1:8.5. The designed system showed higher sensitivity and specificity over enzyme linked immunosorbent assay (ELISA) with a limit of detection of 0.13μgmL(-1) and 93% and 94% sensitivity and specificity, respectively. As designed sensor is rapid, sensitive, specific and efficient in detecting CTV, this could be envisioned for diagnostic applications, surveillance and plant certification program.
A DNA micro-optode for dengue virus detection was developed based on the sandwich hybridization strategy of DNAs on succinimide-functionalized poly(n-butyl acrylate) (poly(nBA-NAS)) microspheres. Gold nanoparticles (AuNPs) with an average diameter of ~20 nm were synthesized using a centrifugation-based method and adsorbed on the submicrometer-sized polyelectrolyte-coated poly(styrene-co-acrylic acid) (PSA) latex particles via an electrostatic method. The AuNP-latex spheres were attached to the thiolated reporter probe (rDNA) by Au-thiol binding to functionalize as an optical gold-latex-rDNA label. The one-step sandwich hybridization recognition involved a pair of a DNA probe, i.e., capture probe (pDNA), and AuNP-PSA reporter label that flanked the target DNA (complementary DNA (cDNA)). The concentration of dengue virus cDNA was optically transduced by immobilized AuNP-PSA-rDNA conjugates as the DNA micro-optode exhibited a violet hue upon the DNA sandwich hybridization reaction, which could be monitored by a fiber-optic reflectance spectrophotometer at 637 nm. The optical genosensor showed a linear reflectance response over a wide cDNA concentration range from 1.0 × 10-21 M to 1.0 × 10-12 M cDNA (R2 = 0.9807) with a limit of detection (LOD) of 1 × 10-29 M. The DNA biosensor was reusable for three consecutive applications after regeneration with mild sodium hydroxide. The sandwich-type optical biosensor was well validated with a molecular reverse transcription polymerase chain reaction (RT-PCR) technique for screening of dengue virus in clinical samples, e.g., serum, urine, and saliva from dengue virus-infected patients under informed consent.
Epizootic ulcerative syndrome (EUS) is a devastating fish disease caused by the fungus, Aphanomyces invadans. Rapid diagnosis of EUS is needed to control and treat this highly invasive disease. The current diagnostic methods for EUS are labor intensive. We have developed a highly sensitive and specific electrochemical genosensor towards the 18S rRNA and internal transcribed spacer regions of A. invadans. Multiple layers of latex were synthesized with the help of polyelectrolytes, and labeled with gold nanoparticles to enhance sensitivity. The gold-latex spheres were functionalized with specific DNA probes. We describe here the novel application of this improved platform for detection of PCR product from real sample of A. invadans using a premix sandwich hybridization assay. The premix assay was easier, more specific and gave higher sensitivity of one log unit when compared to the conventional method of step-by-step hybridization. The limit of detection was 0.5 fM (4.99 zmol) of linear target DNA and 1 fM (10 amol) of PCR product. The binding positions of the probes to the PCR amplicons were optimized for efficient hybridization. Probes that hybridized close to the 5' or 3' terminus of the PCR amplicons gave the highest signal due to minimal steric hindrance for hybridization. The genosensor is highly suitable as a surveillance and diagnostic tool for EUS in the aquaculture industry.
Vibrio cholerae is a Gram-negative bacterium that causes cholera, a diarrheal disease. Cholera is widespread in poor, under-developed or disaster-hit countries that have poor water sanitation. Hence, a rapid detection method for V. cholerae in the field under these resource-limited settings is required. In this paper, we describe the development of an electrochemical genosensor assay using lyophilized gold nanoparticles/latex microsphere (AuNPs-PSA) reporter label. The reporter label mixture was prepared by lyophilization of AuNPs-PSA-avidin conjugate with different types of stabilizers. The best stabilizer was 5% sorbitol, which was able to preserve the dried conjugate for up to 30 days. Three methods of DNA hybridization were compared and the one-step sandwich hybridization method was chosen as it was fastest and highly specific. The performance of the assay using the lyophilized reagents was comparable to the wet form for detection of 1aM to 1fM of linear target DNA. The assay was highly specific for V. cholerae, with a detection limit of 1fM of PCR products. The ability of the sensor is to detect LAMP products as low as 50ngµl(-1). The novel lyophilized AuNPs-PSA-avidin reporter label with electrochemical genosensor detection could facilitate the rapid on-site detection of V. cholerae.
The detection of phenolic compounds, i.e. resorcinol (RC) catechol (CC) and hydroquinone (HQ) are important due to their extremely hazardous impact and poor environmental degradation. In this work, a novel and sensitive composite of electrochemically reduced graphene oxide-poly(Procion Red MX-5B)/gold nanoparticles modified glassy carbon electrode (GCE/ERGO-poly(PR)/AuNPs) was assembled for voltammetric detection of benzenediol isomers (RC, CC, and HQ). The nanocomposite displayed high peak currents towards the oxidation of RC, HQ, and CC compared to non-modified GCE. The peak-to-peak separations were 0.44 and 0.10 V for RC-CC and CC-HQ, respectively. The limit of detections were 53, 53, and 79 nM for HQ, CC, and RC with sensitivities of 4.61, 4.38, and 0.56 μA/μM (S/N = 3), respectively. The nanocomposite displayed adequate reproducibility, besides good stability and acceptable recoveries for wastewater and cosmetic samples analyses.
Clenbuterol (CLB) is an antibiotic and illegal growth promoter drug that has a long half-life and easily remains as residue and contaminates the animal-based food product that leads to various health problems. In this work, electrochemical immunosensor based on poly(3,4-ethylenedioxythiophene)/graphene oxide (PEDOT/GO) modified screen-printed carbon electrode (SPCE) for CLB detection was developed for antibiotic monitoring in a food product. The modification of SPCE with PEDOT/GO as a sensor platform was performed through electropolymerization, while the electrochemical assay was accomplished while using direct competitive format in which the free CLB and clenbuterol-horseradish peroxidase (CLB-HRP) in the solution will compete to form binding with the polyclonal anti-clenbuterol antibody (Ab) immobilized onto the modified electrode surface. A linear standard CLB calibration curve with R² = 0.9619 and low limit of detection (0.196 ng mL-1) was reported. Analysis of milk samples indicated that this immunosensor was able to detect CLB in real samples and the results that were obtained were comparable with enzyme-linked immunosorbent assays (ELISA).
Brain-eating amoebae cause devastating infections in the central nervous system of humans, resulting in a mortality rate of 95%. There are limited effective therapeutic options available clinically for treating granulomatous amoebic encephalitis and primary amoebic meningoencephalitis caused by Acanthamoeba castellanii (A. castellanii) and Naegleria fowleri (N. fowleri), respectively. Here, we report for the first time that guanabenz conjugated to gold and silver nanoparticles has significant antiamoebic activity against both A. castellanii and N. fowleri. Gold and silver conjugated guanabenz nanoparticles were synthesized by the one-phase reduction method and were characterized by ultraviolet-visible spectrophotometry and atomic force microscopy. Both metals were facilely stabilized by the coating of guanabenz, which was examined by surface plasmon resonance determination. The average size of gold nanoconjugated guanabenz was found to be 60 nm, whereas silver nanoparticles were produced in a larger size distribution with the average diameter of around 100 nm. Guanabenz and its noble metal nanoconjugates exhibited potent antiamoebic effects in the range of 2.5 to 100 μM against both amoebae. Nanoparticle conjugation enhanced the antiamoebic effects of guanabenz, as more potent activity was observed at a lower effective concentration (2.5 and 5 μM) compared to the drug alone. Moreover, encystation and excystation assays revealed that guanabenz inhibits the interconversion between the trophozoite and cyst forms of A. castellanii. Cysticdal effects against N. fowleri were also observed. Notably, pretreatment of A. castellanii with guanabenz and its nanoconjugates exhibited a significant reduction in the host cell cytopathogenicity from 65% to 38% and 2% in case of gold and silver nanoconjugates, respectively. Moreover, the cytotoxic evaluation of guanabenz and its nanoconjugates revealed negligible cytotoxicity against human cells. Guanabenz is already approved for hypertension and crosses the blood-brain barrier; the results of our current study suggest that guanabenz and its conjugated gold and silver nanoparticles can be repurposed as a potential drug for treating brain-eating amoebic infections.
This work explores Electrochemical Impedance Spectroscopy (EIS) detection for a highly-sensitive quantification of prostate-specific antigen (PSA) in Faradaic (f-EIS) and non-Faradaic modes (nf-EIS). Immobilization of monoclonal antibody specific to PSA (anti-PSA) was performed using 1-ethyl-3-dimethylaminopropylcarbodiimide hydrochloride and N-hydroxysuccinimide crosslinking agents in order to conjugate carboxylic (-COOH) terminated group of 16-Mercaptoundecanoic acid with amine (-NH3+) on anti-PSA epitope. This approach offers simple and efficient approach to form a strong, covalently bound thiol-gold (SAu) for a reliable SAM layer formation. Studies on the topographic of pristine Au-IDE surface were performed by Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy techniques, meanwhile a 3-dimensional optical surface profiler, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy techniques were used to validate the successful functionalization steps on the sensor transducer surface. Detection of PSA in f-EIS mode was carried out by measuring the response in charge transfer resistance (Rct) and impedance change (Z), meanwhile in nf-EIS mode, the changes in device capacitance was monitored. In f-EIS mode, the sensor reveals a logarithmic detection of PSA in a range of 100 ng/ml down to 0.01 ng/ml in Phosphate Buffered Saline with a recorded sensitivity of 2.412 kΩ/log10 ([PSA] ng/ml) and the limit of detection (LOD) down to 0.01 ng/ml. The nf-EIS detection mode yields a logarithmic detection range of 5000 ng/ml down to 0.5 ng/ml, with a sensitivity of 8.570 nF/log10 ([PSA] ng/ml) and an LOD of 0.5 ng/ml. The developed bio-assay yields great device stability, specificity to PSA and repeatability of detection that would pave its way for the future development into portable lab-on-chip bio-sensing system.
In this study, an electrochemical sensor was fabricated based on gold nanoparticles/ ethylenediamine/ multi-wall carbon-nanotubes modified gold electrode (AuNPs/en/MWCNTs/AuE) for determination of valrubicin in biological samples. Valrubicin was effectively accumulated on the surface of AuNPs/en/MWCNTs/AuE and produced a pair of redox peaks at around 0.662 and 0.578V (vs. Ag/AgCl) in citrate buffer (pH4.0). The electrochemical parameters including pH, buffer, ionic strength, scan rate and size of AuNPs have been optimized. There was a good linear correlation between cathodic peak current and concentration of valrubicin in the range of 0.5 to 80.0μmolL(-1) with the detection limit of 0.018μmolL(-1) in citrate buffer (pH4.0) and 0.1molL(-1) KCl. Finally, the constructed sensor was successfully applied for determination of valrubicin in human urine and blood serum. In further studies, the different sequences of single stranded DNA probes have been immobilized on the surface of AuNPs decorated on MWCNTs to study the interaction of oligonucleotides with valrubicin.