Limits...
Ordered Monolayer Gold Nano-urchin Structures and Their Size Induced Control for High Gas Sensing Performance.

Sabri YM, Kandjani AE, Ippolito SJ, Bhargava SK - Sci Rep (2016)

Bottom Line: It was found that the sensitivity and selectivity of the sensor device is enhanced by increasing the size of the nanospikes on the Au-NUs.The sensor had 98% accuracy, 92% recovery, 96% precision (repeatability) and significantly, showed the highest sensitivity reported to date, resulting in a limit of detection (LoD) of only 32 μg/m3 at 75 °C.When compared to the control counterpart, the accuracy and sensitivity of the Au-NU-12 min was enhanced by ~2 and ~5 times, respectively.

View Article: PubMed Central - PubMed

Affiliation: Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne, VIC 3001 (Australia).

ABSTRACT
The synthesis of ordered monolayers of gold nano-urchin (Au-NU) nanostructures with controlled size, directly on thin films using a simple electrochemical method is reported in this study. In order to demonstrate one of the vast potential applications, the developed Au-NUs were formed on the electrodes of transducers (QCM) to selectively detect low concentrations of elemental mercury (Hg(0)) vapor. It was found that the sensitivity and selectivity of the sensor device is enhanced by increasing the size of the nanospikes on the Au-NUs. The Au-NU-12 min QCM (Au-NUs with nanospikes grown on it for a period of 12 min) had the best performance in terms of transducer based Hg(0) vapor detection. The sensor had 98% accuracy, 92% recovery, 96% precision (repeatability) and significantly, showed the highest sensitivity reported to date, resulting in a limit of detection (LoD) of only 32 μg/m3 at 75 °C. When compared to the control counterpart, the accuracy and sensitivity of the Au-NU-12 min was enhanced by ~2 and ~5 times, respectively. The results demonstrate the excellent activity of the developed materials which can be applied to a range of applications due to their long range order, tunable size and ability to form directly on thin-films.

No MeSH data available.


Related in: MedlinePlus

(a) Schematic representing the QCM transducer modification process a-1) Depositon of Ti electrodes on quartz substrates through e-beam evaporation in order to form Ti QCMs followed by a-2) the transfer of self-assembled PSNS on the Ti electrodes of the QCMs followed by a-3) deposition of gold through e-beam evaporation to develop Au-MNM and finally a-4) electrochemical deposition of nanospikes to form gold nano-urchins (Au-NUs); and SEM images of (b) close-packed Au-MNM, (c) Au-NU-6 min, (d) Au-NU-8 min, (e) Au-NU-10 min, (f) Au-NU-12 min and (g) Au-NU-15 min, all deposited directly on the Ti electrodes of the QCM transducers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4835752&req=5

f1: (a) Schematic representing the QCM transducer modification process a-1) Depositon of Ti electrodes on quartz substrates through e-beam evaporation in order to form Ti QCMs followed by a-2) the transfer of self-assembled PSNS on the Ti electrodes of the QCMs followed by a-3) deposition of gold through e-beam evaporation to develop Au-MNM and finally a-4) electrochemical deposition of nanospikes to form gold nano-urchins (Au-NUs); and SEM images of (b) close-packed Au-MNM, (c) Au-NU-6 min, (d) Au-NU-8 min, (e) Au-NU-10 min, (f) Au-NU-12 min and (g) Au-NU-15 min, all deposited directly on the Ti electrodes of the QCM transducers.

Mentions: Figure 1a shows the summary of the fabrication process of Au-NU directly on QCM transducers. Briefly, a 300 nm Ti film was e-beam evaporated on each of the two sides of the optically polished quartz substrates to form the two electrodes required for oscillation of the crystal (Fig. 1a-1). A monolayer of monodispersed polystyrene nanospheres (PSNS) was deposited directly on the QCM substrates (Fig. 1a-2) and a 100 nm Au film deposition using e-beam evaporation was then followed (Fig. 1a-3) thereby forming gold evaporated monodispersed nanosphere monolayer (Au-MNM). One QCM having no PSNS was also fabricated as the control device and is referred to as Au-control. The Au-NUs were then formed following a one-step electrodeposition of gold nanospikes on the Au-MNM (Fig. 1a-4) for various periods of time. Figure 1b shows the SEM image of the Au-MNM deposited directly on the QCM transducers. The PSNS are observed to be monodispersed, have size of ~500 nm and have formed long-range ordered hexagonally close-packed monolayer on the QCM transducer’s Ti electrode. The SEM images of Au-NU having different sizes are shown in Fig. 1c–g. The different sizes of spikes on the nano-urchins were formed by electrochemical deposition of Au-nanospikes for a period of 6 (c), 8 (d), 10 (e), 12 (f) and 15 (g) minutes. It can be observed that as the electrochemical deposition time increased, the size of the nanospikes forming nano-urchins also increased reaching sizes of 300 nm and 1.5 μm for deposition times of 6 and 15 minutes, respectively. It is also observed that by increasing the deposition time, the electrodeposited Au nanostructures tend to grow to more defined spikes with relatively sharper tips and with saw-teeth shaped edges and increasing base size. These observations are better demonstrated in the higher SEM magnification of each sample that is shown in the Supplementary information (Fig. S1). The monolayer order packing quality and the growth structure of the nanospikes on Au-MNM monolayers, low magnification and side view SEM images are shown in Fig. 2. In Fig. 2a, the packed monolayer formation of PS monodispersed nanospheres is demonstrated where only minor packing faults observed due to small variations in size as well as some drying effects that occurred during monolayer formation process. The successful formation of a single layer of close-packed PSNS can be clearly seen from Fig. 2b where a side view SEM image of Au-MNM is presented. Although some packing faults have induced discrete close packed islands, using a fast Fourier transformation (FFT) showed that distinct and uniform hexagonal spots have been formed on the substrate (see inset in Fig. 2a)53. The low magnification SEM image for Au-NU-12 min sample is shown in Fig. 2c. This image clearly shows that the Au nanospikes growth can be considered as an even process over the whole QCM sensitive layer. The side view image of Au-NU-12 min is shown in Fig. 2d which provides further insight into the growth and formation of the packed urchin morphologies. The nanospikes are observed to start their growth on the e-beam evaporated semispherical Au shell of the Au-MNM samples. Due to the better access to the electrodeposition solution and more intense electrical field on the top of the Au-MNM, the spikes starts growing from the top-most area of these semispherical shells. Furthermore, as the structures have highly ordered packing arrangement in the monolayer formed, the nanospikes tend to point outwards, near-perpendicular to the horizontal plane of the electrodes.


Ordered Monolayer Gold Nano-urchin Structures and Their Size Induced Control for High Gas Sensing Performance.

Sabri YM, Kandjani AE, Ippolito SJ, Bhargava SK - Sci Rep (2016)

(a) Schematic representing the QCM transducer modification process a-1) Depositon of Ti electrodes on quartz substrates through e-beam evaporation in order to form Ti QCMs followed by a-2) the transfer of self-assembled PSNS on the Ti electrodes of the QCMs followed by a-3) deposition of gold through e-beam evaporation to develop Au-MNM and finally a-4) electrochemical deposition of nanospikes to form gold nano-urchins (Au-NUs); and SEM images of (b) close-packed Au-MNM, (c) Au-NU-6 min, (d) Au-NU-8 min, (e) Au-NU-10 min, (f) Au-NU-12 min and (g) Au-NU-15 min, all deposited directly on the Ti electrodes of the QCM transducers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835752&req=5

f1: (a) Schematic representing the QCM transducer modification process a-1) Depositon of Ti electrodes on quartz substrates through e-beam evaporation in order to form Ti QCMs followed by a-2) the transfer of self-assembled PSNS on the Ti electrodes of the QCMs followed by a-3) deposition of gold through e-beam evaporation to develop Au-MNM and finally a-4) electrochemical deposition of nanospikes to form gold nano-urchins (Au-NUs); and SEM images of (b) close-packed Au-MNM, (c) Au-NU-6 min, (d) Au-NU-8 min, (e) Au-NU-10 min, (f) Au-NU-12 min and (g) Au-NU-15 min, all deposited directly on the Ti electrodes of the QCM transducers.
Mentions: Figure 1a shows the summary of the fabrication process of Au-NU directly on QCM transducers. Briefly, a 300 nm Ti film was e-beam evaporated on each of the two sides of the optically polished quartz substrates to form the two electrodes required for oscillation of the crystal (Fig. 1a-1). A monolayer of monodispersed polystyrene nanospheres (PSNS) was deposited directly on the QCM substrates (Fig. 1a-2) and a 100 nm Au film deposition using e-beam evaporation was then followed (Fig. 1a-3) thereby forming gold evaporated monodispersed nanosphere monolayer (Au-MNM). One QCM having no PSNS was also fabricated as the control device and is referred to as Au-control. The Au-NUs were then formed following a one-step electrodeposition of gold nanospikes on the Au-MNM (Fig. 1a-4) for various periods of time. Figure 1b shows the SEM image of the Au-MNM deposited directly on the QCM transducers. The PSNS are observed to be monodispersed, have size of ~500 nm and have formed long-range ordered hexagonally close-packed monolayer on the QCM transducer’s Ti electrode. The SEM images of Au-NU having different sizes are shown in Fig. 1c–g. The different sizes of spikes on the nano-urchins were formed by electrochemical deposition of Au-nanospikes for a period of 6 (c), 8 (d), 10 (e), 12 (f) and 15 (g) minutes. It can be observed that as the electrochemical deposition time increased, the size of the nanospikes forming nano-urchins also increased reaching sizes of 300 nm and 1.5 μm for deposition times of 6 and 15 minutes, respectively. It is also observed that by increasing the deposition time, the electrodeposited Au nanostructures tend to grow to more defined spikes with relatively sharper tips and with saw-teeth shaped edges and increasing base size. These observations are better demonstrated in the higher SEM magnification of each sample that is shown in the Supplementary information (Fig. S1). The monolayer order packing quality and the growth structure of the nanospikes on Au-MNM monolayers, low magnification and side view SEM images are shown in Fig. 2. In Fig. 2a, the packed monolayer formation of PS monodispersed nanospheres is demonstrated where only minor packing faults observed due to small variations in size as well as some drying effects that occurred during monolayer formation process. The successful formation of a single layer of close-packed PSNS can be clearly seen from Fig. 2b where a side view SEM image of Au-MNM is presented. Although some packing faults have induced discrete close packed islands, using a fast Fourier transformation (FFT) showed that distinct and uniform hexagonal spots have been formed on the substrate (see inset in Fig. 2a)53. The low magnification SEM image for Au-NU-12 min sample is shown in Fig. 2c. This image clearly shows that the Au nanospikes growth can be considered as an even process over the whole QCM sensitive layer. The side view image of Au-NU-12 min is shown in Fig. 2d which provides further insight into the growth and formation of the packed urchin morphologies. The nanospikes are observed to start their growth on the e-beam evaporated semispherical Au shell of the Au-MNM samples. Due to the better access to the electrodeposition solution and more intense electrical field on the top of the Au-MNM, the spikes starts growing from the top-most area of these semispherical shells. Furthermore, as the structures have highly ordered packing arrangement in the monolayer formed, the nanospikes tend to point outwards, near-perpendicular to the horizontal plane of the electrodes.

Bottom Line: It was found that the sensitivity and selectivity of the sensor device is enhanced by increasing the size of the nanospikes on the Au-NUs.The sensor had 98% accuracy, 92% recovery, 96% precision (repeatability) and significantly, showed the highest sensitivity reported to date, resulting in a limit of detection (LoD) of only 32 μg/m3 at 75 °C.When compared to the control counterpart, the accuracy and sensitivity of the Au-NU-12 min was enhanced by ~2 and ~5 times, respectively.

View Article: PubMed Central - PubMed

Affiliation: Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University, GPO Box 2476V, Melbourne, VIC 3001 (Australia).

ABSTRACT
The synthesis of ordered monolayers of gold nano-urchin (Au-NU) nanostructures with controlled size, directly on thin films using a simple electrochemical method is reported in this study. In order to demonstrate one of the vast potential applications, the developed Au-NUs were formed on the electrodes of transducers (QCM) to selectively detect low concentrations of elemental mercury (Hg(0)) vapor. It was found that the sensitivity and selectivity of the sensor device is enhanced by increasing the size of the nanospikes on the Au-NUs. The Au-NU-12 min QCM (Au-NUs with nanospikes grown on it for a period of 12 min) had the best performance in terms of transducer based Hg(0) vapor detection. The sensor had 98% accuracy, 92% recovery, 96% precision (repeatability) and significantly, showed the highest sensitivity reported to date, resulting in a limit of detection (LoD) of only 32 μg/m3 at 75 °C. When compared to the control counterpart, the accuracy and sensitivity of the Au-NU-12 min was enhanced by ~2 and ~5 times, respectively. The results demonstrate the excellent activity of the developed materials which can be applied to a range of applications due to their long range order, tunable size and ability to form directly on thin-films.

No MeSH data available.


Related in: MedlinePlus