Publications by authors named "Ahmad E Kandjani"

10 Publications

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Liquid Crystal-Mediated 3D Printing Process to Fabricate Nano-Ordered Layered Structures.

ACS Appl Mater Interfaces 2021 Jun 10;13(24):28627-28638. Epub 2021 Jun 10.

School of Chemical Engineering, University of New South Wales (UNSW), Sydney 2052, New South Wales, Australia.

The emergence of three-dimensional (3D) printing promises a disruption in the design and on-demand fabrication of smart structures in applications ranging from functional devices to human organs. However, the scale at which 3D printing excels is within macro- and microlevels and principally lacks the spatial ordering of building blocks at nanolevels, which is vital for most multifunctional devices. Herein, we employ liquid crystal (LC) inks to bridge the gap between the nano- and microscales in a single-step 3D printing. The LC ink is prepared from mixtures of LCs of nanocellulose whiskers and large sheets of graphene oxide, which offers a highly ordered laminar organization not inherently present in the source materials. LC-mediated 3D printing imparts the fine-tuning required for the design freedom of architecturally layered systems at the nanoscale with intricate patterns within the 3D-printed constructs. This approach empowered the development of a high-performance humidity sensor composed of self-assembled lamellar organization of NC whiskers. We observed that the NC whiskers that are flat and parallel to each other in the laminar organization allow facile mass transport through the structure, demonstrating a significant improvement in the sensor performance. This work exemplifies how LC ink, implemented in a 3D printing process, can unlock the potential of individual constituents to allow macroscopic printing architectures with nanoscopic arrangements.
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http://dx.doi.org/10.1021/acsami.1c05025DOI Listing
June 2021

Low-Temperature Hydrogen Sensor: Enhanced Performance Enabled through Photoactive Pd-Decorated TiO Colloidal Crystals.

ACS Sens 2020 12 1;5(12):3902-3914. Epub 2020 Dec 1.

Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Science, RMIT University, Melbourne 3001, Victoria, Australia.

The high demand for H gas sensors is not just limited to industrial process control and leak detection applications but also extends to the food and medical industry to determine the presence of various types of bacteria or underlying medical conditions. For instance, sensing of H at low concentrations (<10 ppm) is essential for developing breath analyzers for the noninvasive diagnosis of some gastrointestinal diseases. However, there are major challenges to overcome in order to achieve high sensitivity and hence low limit of detection (LoD) toward H. In this study, it is demonstrated that light-assisted amperometric gas sensors employing sensitive layers based on Pd-decorated TiO long-range ordered crystals can achieve excellent H sensing performance. This unique combination of materials and novel layered structure enables the detection of H gas down to 50 ppm with highly promising LoD capabilities. The sensor response profiles revealed that the sensor's signal-to-noise ratio was higher in the presence of light when operated with a 9 V bias (relative to other conditions used), producing a LoD of only 3.5 ppm at an operating temperature of 33 °C. The high performance of the sensor makes it attractive for applications that require low-level (ppm as opposed to conventional % levels) H gas detection. Most importantly, the developed sensor exhibited high selectivity (>93%) toward H over other gas species such as CO, CHO, CHO, CHCHO, and NO, which are commonly found to coexist in the environment.
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http://dx.doi.org/10.1021/acssensors.0c01387DOI Listing
December 2020

Zinc Titanate Nanoarrays with Superior Optoelectrochemical Properties for Chemical Sensing.

ACS Appl Mater Interfaces 2019 Aug 5;11(32):29255-29267. Epub 2019 Aug 5.

School of Engineering , RMIT University , Melbourne 3001 , Victoria , Australia.

In this report, the gas sensing performance of zinc titanate (ZnTiO) nanoarrays (NAs) synthesized by coating hydrothermally formed zinc oxide (ZnO) NAs with TiO using low-temperature chemical vapor deposition is presented. By controlling the annealing temperature, diffusion of ZnO into TiO forms a mixed oxide of ZnTiO NAs. The uniformity and the electrical properties of ZnTiO NAs made them ideal for light-activated acetone gas sensing applications for which such materials are not well studied. The acetone sensing performance of the ZnTiO NAs is tested by biasing the sensor with voltages from 0.1 to 9 V dc in an amperometric mode. An increase in the applied bias was found to increase the sensitivity of the device toward acetone under photoinduced and nonphotoinduced (dark) conditions. When illuminated with 365 nm UV light, the sensitivity was observed to increase by 3.4 times toward 12.5 ppm acetone at 350 °C with an applied bias of 9 V, as compared to dark conditions. The sensor was also observed to have significantly reduced the adsorption time, desorption time, and limit of detection (LoD) when excited by the light source. For example, LoD of the sensor in the dark and under UV light at 350 °C with a 9 V bias is found to be 80 and 10 ppb, respectively. The described approach also enabled acetone sensing at an operating temperature down to 45 °C with a repeatability of >99% and a LoD of 90 ppb when operated under light, thus indicating that the ZnTiO NAs are a promising material for low concentration acetone gas sensing applications.
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http://dx.doi.org/10.1021/acsami.9b08704DOI Listing
August 2019

CoO needles on Au honeycomb as a non-invasive electrochemical biosensor for glucose in saliva.

Biosens Bioelectron 2019 Sep 26;141:111479. Epub 2019 Jun 26.

Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Science, RMIT University, Melbourne, Victoria, 3001, Australia. Electronic address:

While glucose monitoring technology is widely available, the continued prevalence of diabetes around the world coupled with its debilitating effects continues to grow. The significant limitations which exist in the current technology, instils the need for materials capable of non-invasive glucose detection. In this study a unique non-enzymatic electrochemical glucose sensor was developed, utilising a gold honeycomb-like framework upon which sharp CoO needles are anchored. This composite nanomaterial demonstrates excellent sensing performance in glucose concentrations ranging between 20 μM and 4 mM, exceeding the range required for non-invasive glucose sensing. In conjunction with this high sensitivity (2.014 mA mM·cm), the material possesses excellent selectivity towards glucose for commonly interfering physiological species such as uric acid and ascorbic acid. Glucose detection in synthetic saliva was then performed showing excellent capability in the low concentration range (20 μM-1 mM) for non-invasive sensing performance. Further tests showed good selectivity of the sensor in physiological contaminants commonly found in saliva such as cortisol and dopamine. This development provides excellent scope to create next-generation non-invasive diabetes monitoring platforms, with excellent performance when detecting low glucose concentrations in complex solutions such as saliva.
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http://dx.doi.org/10.1016/j.bios.2019.111479DOI Listing
September 2019

Using colloidal lithography to control the formation of gas sorption sites through galvanic replacement reaction.

J Colloid Interface Sci 2019 Jul 1;547:199-205. Epub 2019 Apr 1.

Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Science, RMIT University, Melbourne 3000, Australia. Electronic address:

Using colloidal lithography, a series of inverted long-range ordered crystals (i-LROCs) of Pd honeycombs were fabricated on quartz crystal microbalance (QCM) sensors. The structures formed provided the required platform for the proceeding galvanic replacement reaction (GR) process to generate seamless Au nanoparticle deposits throughout the i-LROC. The results showed that controlling the dimensions of the pores in the developed Pd i-LROCs is important in the formation of gold deposition sites on the uniform structures through the GR reaction process. The developed Pd/Au i-LROC deposited sensors showed significant enhancement in the sensitivity toward Hg vapor when compared to pure Pd structures, with limit of detection improving from 60.0 to 13.7 µg/m, respectively. Furthermore, a significant improvement in the modified sensor's selectivity toward Hg in the presence of other industrial related gas species was observed which is attributed to the addition of Au to the Pd structures through GR reaction.
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http://dx.doi.org/10.1016/j.jcis.2019.04.001DOI Listing
July 2019

Functionalization of Elongated Tetrahexahedral Au Nanoparticles and Their Antimicrobial Activity Assay.

ACS Appl Mater Interfaces 2019 Apr 1;11(14):13450-13459. Epub 2019 Apr 1.

Department of Biotechnology and Genetic Engineering , Jahangirnagar University , Savar , Dhaka 1342 , Bangladesh.

Gold nanoparticles are inert for the human body, and therefore, they have been functionalized to provide them with antibacterial properties. Here, elongated tetrahexahedral (ETHH) Au nanoparticles were synthesized, characterized, and functionalized with lipoic acid (LA), a natural antioxidant with a terminal carboxylic acid and a dithiolane ring, to generate ETHH-LA Au nanoparticles. The antioxidant activity of Au nanoparticles was investigated in vitro, showing that LA enhances the 2,2-diphenyl-1-picrylhydrazyl free-radical scavenging and Fe ion reducing activity of ETHH-LA at higher amounts. The antimicrobial propensities of the nanoparticles were investigated against Gram-positive ( Bacillus subtilis) and Gram-negative ( Escherichia coli) bacteria through propidium iodide assay as well as disk diffusion assay. ETHH-LA Au nanoparticles showed significantly higher antimicrobial activity against B. subtilis compared with E. coli. Furthermore, ETHH-LA Au nanoparticles also showed significantly better antimicrobial activity against both bacterial strains when compared with ETHH. ETHH Au nanoparticles also bring about the oxidation of bacterial cell membrane fatty acids and produce lipid peroxides. ETHH-LA showed higher lipid peroxidation potential than that of ETHH against both bacteria tested. The hemolytic potential of Au nanoparticles was investigated using human red blood cells and ETHH-LA showed reduced hemolytic activity than that of ETHH. The cytotoxicity of Au nanoparticles was investigated using human cervical cancer cells, HeLa, and ETHH-LA Au nanoparticles showed reduced cytotoxicity than that of ETHH. Taken together, LA enhances the antimicrobial activity of ETHH Au nanoparticles and Au nanoparticles interact with the bacteria through electrostatic interactions as well as hydrophobic interactions and damage the bacterial cell wall followed by oxidation of cell membrane fatty acids.
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http://dx.doi.org/10.1021/acsami.9b02279DOI Listing
April 2019

Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance.

Nat Commun 2018 11 29;9(1):5070. Epub 2018 Nov 29.

Intelligent Polymer Research Institute & ARC Centre of Excellence for Electromaterials Science, Australian Institute for Innovative Materials, University of Wollongong, Wollongong, NSW, 2522, Australia.

Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.
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http://dx.doi.org/10.1038/s41467-018-07396-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6265250PMC
November 2018

Oxygen-deficient photostable CuO for enhanced visible light photocatalytic activity.

Nanoscale 2018 Mar;10(13):6039-6050

Ian Potter NanoBioSensing Facility, NanoBiotechnology Research Laboratory, School of Science, RMIT University, Melbourne, VIC 3000, Australia.

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron-hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(i)-triethylamine [Cu(i)-TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.
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http://dx.doi.org/10.1039/C7NR08388BDOI Listing
March 2018

1,4-Dihydropyrrolo[3,2-b]pyrroles as a Single Component Photoactive Layer: A New Paradigm for Broadband Detection.

ACS Appl Mater Interfaces 2017 Aug 10;9(33):27875-27882. Epub 2017 Aug 10.

School of Engineering (SoE), ‡School of Sciences, and §Centre for Advanced Materials and Industrial Chemistry, RMIT University , 124 La Trobe St, Melbourne, Victoria 3000, Australia.

Single component organic photodetectors capable of broadband light sensing represent a paradigm shift for designing flexible and inexpensive optoelectronic devices. The present study demonstrates the application of a new quadrupolar 1,4-dihydropyrrolo[3,2-b]pyrrole derivative with spectral sensitivity across 350-830 nm as a potential broadband organic photodetector (OPD) material. The amphoteric redox characteristics evinced from the electrochemical studies are exploited to conceptualize a single component OPD with ITO and Al as active electrodes. The photodiode showed impressive broadband photoresponse to monochromatic light sources of 365, 470, 525, 589, 623, and 830 nm. Current density-voltage (J-V) and transient photoresponse studies showed stable and reproducible performance under continuous on/off modulations. The devices operating in reverse bias at 6 V displayed broad spectral responsivity (R) and very good detectivity (D*) peaking a maximum 0.9 mA W and 1.9 × 10 Jones (at 623 nm and 500 μW cm) with a fast rise and decay times of 75 and 140 ms, respectively. Low dark current densities ranging from 1.8 × 10 Acm at 1 V to 7.2 × 10 A cm at 6 V renders an operating range to amplify the photocurrent signal, spectral responsivity, and detectivity. Interestingly, the fabricated OPDs display a self-operational mode which is rarely reported for single component organic systems.
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http://dx.doi.org/10.1021/acsami.7b08906DOI Listing
August 2017

Synergistic influence of polyoxometalate surface corona towards enhancing the antibacterial performance of tyrosine-capped Ag nanoparticles.

Nanoscale 2014 Jan;6(2):758-65

NanoBiotechnology Research Lab (NBRL), Centre for Advanced Materials & Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne, VIC 3000, Australia.

We illustrate a new strategy to improve the antibacterial potential of silver nanoparticles (AgNPs) by their surface modification with the surface corona of biologically active polyoxometalates (POMs). The stable POM surface corona was achieved by utilising zwitterionic tyrosine amino acid as a pH-switchable reducing and capping agent of AgNPs. The general applicability of this approach was demonstrated by developing surface coronas of phosphotungstic acid (PTA) and phosphomolybdic acid (PMA) around AgNPs. Our investigations on Gram negative bacterium Escherichia coli demonstrate that in conjugation with AgNPs, the surface corona of POMs enhances the physical damage to the bacterial cells due to synergistic antibacterial action of AgNPs and POMs, and the ability of tyrosine-reduced AgNPs (AgNPs(Y)) to act as an excellent carrier and stabiliser for the POMs. The further extension of this study towards Gram positive bacterium Staphylococcus albus showed a similar toxicity pattern, whereas these nanomaterials were found to be biocompatible for PC3 epithelial mammalian cells, suggesting the potential of these materials towards specific antimicrobial targeting for topical wound healing applications. The outcomes of this work show that facile tailorability of nanostructured surfaces may play a considerable role in controlling the biological activities of different nanomaterials.
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http://dx.doi.org/10.1039/c3nr03806hDOI Listing
January 2014
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