Detection of surface enhanced Raman scattering active hotspot using near field scanning optical microscopy

Hotspots are high-intensity electromagnetic zones that form, for example, at the interstitials of plasmonic nanoaggregates, resulting in a considerable rise in the enhancement factor. However, it is inevitable to achieve specific nanometric geometry as well as a suitable technique to capture the details of hotspots. We report near-field surface-enhanced Raman scattering (SERS) spectroscopy of a well-defined gold nanoaggregate of a few nanoparticles adsorbed with a small number of target analytes. A spectrally and spatially resolved SERS measurement setup using an aperture near-field scanning optical microscope (a-NSOM) facilitated the direct observation of localized electromagnetic (EM) fields at the interstitials through SERS. Correlated optical image and corresponding nanometric geometry were captured through the home-built a-NSOM setup. Near-field SERS spectra were recorded at different sites of interest. It was evident that the interstitial positioned at the center of the tetramer provided the most intense Raman scattering, implying the possibility of a SERS-active hotspot therein. SERS bands of the spectrum of the Raman-active dye Rhodamine 6G recorded at the same hotspot coincided well with those reported so far. It was noteworthy that most of the SERS bands in such scenery got enhanced. Such direct observation with high spatial resolution is indispensable to understanding the origin of localized EM fields at "hotspots" and the EM enhancement factor in the SERS process. A finite-difference time-domain (FDTD) analysis was carried out to validate the results.

Understanding the impact of socioeconomic and health factors on geriatric depression: A comparative study in rural and urban Bangladesh

Background and Aims

The prevalence of depression among the elderly is a growing concern, and this study examines the differences between urban and rural areas in terms of geriatric depression.

Methods

Using a two-stage random sampling approach in urban areas and a multistage random sampling approach in rural areas, the study surveyed 944 elderly individuals of both sexes.

Results

The results indicate that the prevalence of depression was high, with 52.5% of the elderly population experiencing mild to severe depression. The study found that increasing age, female gender, nuclear family structure, and involvement of housewives or others were significant factors affecting depression in urban areas, while increasing age and elderly people without spouses were significant factors in rural areas. Additionally, the study identified hearing impairment, asthma, and arthritis as risk factors for depression in rural areas, and bronchitis, heart disease, and thyroid illness as significant factors in urban areas.

Conclusion

These findings highlight the need for policymakers to focus on addressing the mental health needs of older people, particularly women and those without spouses.

Chemiresistive Gas Sensing using Graphene-Metal Oxide Hybrids

Chemiresistive sensing lies in its ability to provide fast, accurate, and reliable detection of various gases in a cost-effective and non-invasive manner. In this context, graphene-functionalized metal oxides play crucial role in hydrogen gas sensing. However, a cost-effective, defect-free, and large production schemes of graphene-based sensors are required for industrial applications. This review focuses on graphene-functionalized metal oxide nanostructures designed for gaseous molecules detection, mainly hydrogen gas sensing applications. For the convenience of the reader and to understand the role of graphene-metal oxide hybrids (GMOH) in gas sensing activities, a brief overview of the properties and synthesis routes of graphene and GMOH have been reported in this paper. Metal oxides play an essential role in the GMOH construct for hydrogen gas sensing. Therefore, various metal oxides-decorated GMOH constructs are detailed in this review as gas sensing platforms, particularly for hydrogen detection. Finally, specific directions for future research works and challenges ahead in designing highly selective and sensitive hydrogen gas sensors have been highlighted. As illustrated in this review, understanding of the metal oxides-decorated GMOH constructs is expected to guide ones in developing emerging hybrid nanomaterials that are suitable for hydrogen gas sensing applications.

Silver-Decorated Silicon Nanostructures: Fabrication and Characterization of Nanoscale Terraces as an Efficient SERS-Active Substrate

Rich and highly dense surface-enhanced Raman (SERS) hotspots available in the SERS-active platform are highly anticipated in SERS measurements. In this work, conventional silicon wafer was treated to have wide exposure to terraces available within the silicon nanostructures (Si-NSs). High-resolution field emission scanning electron microscopic (FESEM) investigations confirmed that the terraces were several microns wide and spread over different steps. These terraces were further decorated with silver nanoparticles (Ag-NPs) of different shapes and sizes to achieve SERS-active hotspots. Based on more than 150 events, a histogram of the size distribution of Ag-NPs indicated a relatively narrow size distribution, 29.64 ± 4.66 nm. The coverage density was estimated to be ~4 × 10¹⁰ cm^-2. The SERS-activity of Ag-NPs -decorated Si-NSs was found to be enhanced with reference to those obtained in pristine Si-NSs. Finite difference time domain models were developed to support experimental observations in view of electromagnetic (EM) near-field distributions. Three archetype models; (i) dimer of same constituent Ag-NPs, (ii) dimer of different constituent Ag-NPs, and (iii) linear trimer of different constituent Ag-NPs were developed. EM near-field distributions were extracted at different incident polarizations. Si-NSs are well-known to facilitate light confinement, and such confinement can be cascaded within different Ag-NPs-decorated terraces of Si-NSs.

Fabrication and Characterization of Au-Decorated MCM-41 Mesoporous Spheres Using Laser-Ablation Technique

This study reports the synthesis of Au-decorated MCM-41 mesoporous nanoparticles using a laser-ablation technique. It was observed that the number of Au attached to MCM-41 nanostructures was dependent on the amount of encapsulated Cationic surfactant (cetyl ammonium bromide (CTAB) volume. The chemical group of the prepared nanoparticles was analyzed by FT-IR spectroscopy, where different absorption peaks corresponding to Au and MCM-41 were observed. The observed band region was ∼1090, 966, 801, 2918, and 1847 cm^-1 for different samples, clearly confirming the successful preparation of MCM-41 with CTAB and Au-decorated MCM-41 nanoparticles using environmentally friendly laser-ablation approach. The surface morphology of the prepared nanoparticles were performed using TEM techniques. The TEM analysis of the MCM-41 specimen showed silica spheres with an average size of around 200 nm. Furthermore, Raman spectroscopy was done to evaluate the chemical structure of the prepared nanoparticles. It was seen that the prepared Au NPs decorated the MCM-41 system facilitated strong Raman peaks of CTAB. In addition, eight distinct Raman peaks were observed in the presence of Au NPs. This new functionalized method using the laser-ablation approach for mesoporous nanoparticles will participate effectively in multiple applications, especially the encapsulated molecule sensing and detection.

Noble Metal-Decorated Nanostructured Zinc Oxide: Strategies to Advance Chemiresistive Hydrogen Gas Sensing

Hydrogen (H₂ ) is known as the key player in the alternative and renewable energy revolution and henceforth H₂ production, transportation, storage and usage have been a major interest of current research. However, due to severe safety concerns, strategies are indispensable to devise superior H₂ sensors, particularly selective and sensitive H₂ sensors. In this personal account, three specific gas sensing constructs; zinc oxide (ZnO) nanostructures-, noble metal nanoparticles-decorated ZnO- and noble metal nanoparticles-decorated ZnO nanostructures on reduced graphene oxide (rGO)-based H₂ sensors have been demonstrated. The dynamic response and H₂ sensing characteristics of ZnO nanostructures-based H₂ sensors were found to be improved compared to those of pristine ZnO. High-resolution field emission scanning electron microscopy (FESEM) confirmed the flower-like nanostructures that had higher surface area around the nanoscale petals. The mechanism behind the superior sensing characteristics of ZnO nanostructures-based H₂ sensor has been demonstrated. Decoration of ZnO nanostructures with noble metal nanoparticles, particularly platinum (Pt) and gold (Au) was observed to be useful in achieving better H₂ sensing performance compared to that of ZnO nanostructures. The Pt- and Au-decorated ZnO nanostructures followed the well-known "Spill-over" mechanism in enhancing the H₂ sensing characteristics. Abundant free electrons/holes generation and higher conductivity are two important parameters for designing selective and sensitive gas sensors. In this context, a hybrid nanocomposite, rGO-ZnO has been developed and decorated with noble metal nanoparticles, particularly Pt and Au. The ultimate sensing material has been characterized and compared to those of pristine ZnO, ZnO nanostructures and Pt- and Au-decorated ZnO for H₂ gas sensing applications. Such systemic and focus strategies is critical not only for developing efficient H₂ gas sensors but also for better understanding the mechanisms underlying such superior performance.

Nanoscale Imaging of Interstitial-dependent Optical Confinement through Near-Field Scanning Optical Microscopy

Exploitation of optical confinement in nanoscale unveils a wealth of information about the structure, optical, electronic, and chemical properties of the materials. However, realizing such confinement by optical microscopy and spectroscopic techniques have remained challenging due to fundamental formulation that is related to the diffraction theory of light. A state-of-art technique, known as near-field scanning optical microscopy (NSOM) has the ability to break such diffraction limitation, as the spatial resolution depends on the near-field probe diameter and the distance between the probe and the surface. A home-built apertured NSOM (a-NSOM) developed in the beginning of NSOM discovery facilitated to investigate N-particles nano-assemblies, where N is two or more. Through surface-sensitive spectroscopy such as surface-enhanced Raman scattering (SERS) and surface-enhanced two-photon-induced photoluminescence (TPI-PL), a correlated optometrology was revealed by taking snapshots of shear-force topography, SERS and TPI-PL simultaneously in single-channel and multi-channel detection system. Here in this "Personal Account" we have decorated near-field optical confinement observed by a-NSOM in three constructs; archetype dimer, nano-assembly of few nanoparticles and long-range two-dimensional (2D) nano-assembly. In the case of dimer, optical confinement was localized and interstitial-dependent whereas coalescence of nearby confinements was reported in few particles nanoaggregate. In the case of 2D nano-assembly, optical confinements were more complex because a nanoparticle was surrounded by six or more adjacent nanoparticles. FDTD simulation were carried out to support and validate the experimental observations. Such observations in nanoscale taking snapshots of nanometric topography and surface-sensitive spectroscopic signal not only inspire us to understand optical confinements in near-field, but also implement the concept in designing miniaturized and efficient system.

Polymer-Templated Durable and Hydrophobic Nanostructures for Hydrogen Gas Sensing Applications

A simple and hands-on one-step process has been implemented to fabricate polymer-templated hydrophobic nanostructures as hydrogen gas sensing platforms. Topographic measurements have confirmed irregular hills and dips of various dimensions that are responsible for creating air bubble pockets that satisfy the Cassie–Baxter state of hydrophobicity. High-resolution field-emission scanning electron microscopy (FESEM) has revealed double-layer structures consisting of fine microscopic flower-like structures of nanoscale petals on the top of base nanostructures. Wetting contact angle (WCA) measurements further revealed the contact angle to be ~142.0° ± 10.0°. Such hydrophobic nanostructures were expected to provide a platform for gas-sensing materials of a higher surface area. From this direction, a very thin layer of palladium, ca. 100 nm of thickness, was sputtered. Thereafter, further topographic and WCA measurements were carried out. FESEM micrographs revealed that microscopic flower-like structures of nanoscale petals remained intact. A sessile drop test reconfirmed a WCA of as high as ~130.0° ± 10.0°. Due to the inherent features of hydrophobic nanostructures, a wider surface area was expected that can be useful for higher target gas adsorption sites. In this context, a customized sensing facility was set up, and H₂ gas sensing performance was carried out. The surface nanostructures were found to be very stable and durable over the course of a year and beyond. A polymer-based hydrophobic gas-sensing platform as investigated in this study will play a dual role in hydrophobicity as well as superior gas-sensing characteristics.

Clusters-based silver nanorings: An active substrate for surface-enhanced Raman scattering

Plasmonic nanostructures, particularly irregular surfaces of ring-like silver (Ag) nanostructures are promising candidates in surface-enhanced Raman scattering (SERS) spectroscopy. In this work, clusters-based Ag nanorings have been fabricated and characterized as SERS-active substrates. The rim of the as-fabricated Ag nanorings was found neither discontinuous nor linear aggregation of nanoparticles. High-resolution field emission scanning electron microscopy (FESEM) revealed that the individual constituent clusters were different from each other, particularly in terms of size and shape in addition to the cases how such clusters were emerged as the edge of the nanoring. Considering the dimensions of the clusters and the arrangement of such clusters as nanorings, it was speculated that the local electromagnetic (EM) near-field distributions would excel and thus enhanced SERS signals would be achieved. Indeed, the inherent features of the nanorings facilitated to achieve SERS enhancement factors as high as 2.1 × 10⁴. SERS-activity of as-fabricated Ag nanorings was confirmed using Rhodamine 6G (R6G) as Raman-active dyes and the enhancement was compared to those obtained from R6G adsorbed on Ag-ZnO/Glass and ZnO/Glass. To the best of our knowledge, this is the first attempt to explore the impact of localized EM near-field within the segments of nanorings through SERS spectroscopy. A model was designed resembling the nanorings under this investigation to simulate EM near-field distributions by finite difference time domain (FDTD) analysis. The dimensions of the model geometry were chosen according to the observations achieved by FESEM. To simplify the simulations, nanoobjects were considered spherical and organized in a periodic fashion, although the constituent clusters of Ag nanorings were found irregular in shape and arrangement. Since EM near-field distribution highly depends on interparticle gaps, three scenarios were implemented, such as, small gap in between two adjacent nanoobjects and adjacent nanoobjects in touch and overlapped. Each configuration was simulated and EM near-field distribution was extracted for s-, p- and 45⁰ of incident polarizations followed by a plausible correlation to SERS enhancements. Such correlated investigations as well as clusters-based Ag nanorings not only inspire the ones to look for cost-effective SERS-active substrate, but also understand the underlying EM mechanism in SERS enhancements.

Study of Antibiotic Sensitivity of Aural Swab and Aetiological Factors of Chronic Otitis Media-Active Mucosal Type

Background: Chronic otitis media (COM) refers to chronic inflammation of mucoperiosteal lining of middle ear cleft resulting in aural discharge and deafness. The objective of this study is to evaluate the antibiotic sensitivity and aetiological factors of COM. Methods: This cross-sectional study was conducted from July 2017 to June 2018 for duration of one year among the patients who attended with COM- active mucosal disease at Department of ENT & Head Neck Surgry, Combined Military Hospital (CMH) Chattogram. Total 50 cases were isolated and among them 5 cases had been suffering from bilateral COM. Aural swab was taken from 55 ears and a predesigned data collection sheet was duly filled up with the information of socioeconomic status of the patient. The laboratory records of every case was systematically organized. The data were analyzed with simple manual analysis using percentage and frequency. Results: About 24% patients were in 31-40 years age group. Out of 50 patients 62% were male. 44% patient lived in barrack. Ear cleaning habit shows, 32% has got the cleaning habit with cloth and stick. Out of 50 patients 5 had bilateral COM. So out of 55 ears, Culture & sensitivity test viewed that Pseudomonas aeruginosa was the most predominant organism - 41.8% followed by S. aureus- 30.9% Antibiotic sensitivity profile shows, 80% cases showing sensitivity to Amikacin then gentamycin-73.3% Resistant 5 cases showed 100% sensitivity to Tazobactum. Again out of 19 cases of Gram positive organism 78.9% were sensitive to Amoxyclav. 3 resistant cases showed 100% sensitivity to Meropenem. Conclusion: By studying this topic we hope to able to make an idea about the aetiological and predisposing factors and antibiotic sensitivity of COM-active mucosal variety. Bangladesh J Otorhinolaryngol 2021; 27(2): 111-116

Half-raspberry-like bimetallic nanoassembly: Interstitial dependent correlated surface plasmon resonances and surface-enhanced Raman spectroscopy

Correlated localized surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and localized electromagnetic (EM) field distributions of pure and modified gold (Au) nanoassemblies have been demonstrated. The Au nanoassemblies were decorated as half-raspberry-like nanostructures by silver (Ag) mists, and the characteristics of their SPR and SERS were observed at the same spatial position with and without decoration. The decoration of Au nanoassemblies was analyzed in-depth and confirmed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). Multifunctional and lab-built microscopy was used to capture correlated SPR and SERS imaging and spectral measurements. Without decoration, strong SPR peaks and enhanced SERS signals were observed, whereas intense plasmon excitation deteriorated with a broadening and diminishing peak and the SERS enhancement dropped at least by 10 fold upon the modification. Preferential enhancement near the edge was observed in the correlated SPR and SERS measurements. The variations in localized SPR, subsequent SERS enhancement, and preferential confinement were speculated concerning localized EM near-field deformation. A typical tetramer with five interstitials was modeled and simulated by finite difference time domain (FDTD) analysis at different incident polarizations. The EM near-field distributions were extracted with and without decoration of constituent interstitials by Ag mists. Without the modification of participating interstitials, the EM near-field distributions were found confined, whereas additional EM near-field confinements were observed in the presence of Ag mists. Such EM near-field deformations due to the modification of constituent interstitials were supposed to broaden and deteriorate SPR characteristics of Au nanoassemblies as observed under this investigation.

Plasmonic Pollen Grain Nanostructures: A Three-Dimensional Surface-Enhanced Raman Scattering (SERS)-Active Substrate

A new route has been developed to design plasmonic pollen grain-like nanostructures (PGNSs) as surface-enhanced Raman scattering (SERS)-active substrate. The nanostructures consisting of silver (Ag) and gold (Au) nanoparticles along with zinc oxide (ZnO) nanoclusters as spacers were found highly SERS-active. The morphology of PGNSs and those obtained in the intermediate stage along with each elemental evolution has been investigated by a high-resolution field emission scanning electron microscopy. The optical band gaps and crystal structure have been identified by UV-vis absorption and X-ray powder diffraction (XRD) measurements, respectively. For PGNSs specimen, three distinct absorption bands related to constituent elements Ag, Au, and ZnO were observed, whereas XRD peaks confirmed the existence of Ag, Au, and ZnO within the composition of PGNSs. SERS-activity of PGNSs was confirmed using Rhodamine 6G (R6G) as Raman-active dyes. Air-cooled solid-state laser kits of 532 nm were used as excitation sources in SERS measurements. SERS enhancement factor was estimated for PGNSs specimen and was found as high as 3.5×10⁶ . Finite difference time domain analysis was carried out to correlate the electromagnetic (EM) near-field distributions with the experiment results achieved under this investigation. EM near-field distributions at different planes were extracted for s-, p- and 45° of incident polarizations. EM near-field distributions for such nanostructures as well as current density distributions under different circumstances were demonstrated and plausible scenarios were elucidated given SERS enhancements. Such generic fabrication route as well as correlated investigation is not only indispensable to realize the potential of SERS applications but also unveil the underneath plasmonic characteristics of complex SERS-active nanostructures.

Frailty indexed classification of Bangladeshi older adults' physio-psychosocial health and associated risk factors- a cross-sectional survey study

BACKGROUND

Frailty is associated with healthy ageing, and it has been identified as a means of measuring older adults' physio-psychosocial health. We know about the ageing trends and common diseases of older adults living in South Asia, but literature to date does not widely feature their health status based on frailty, especially in Bangladesh. This study aims to understand the prevalence of frailty in Bangladeshi older adults; classify their health status; and investigate associated risk factors.

METHODS

A cross-sectional study was conducted in the north-eastern region (i.e. Sylhet City Corporation) of Bangladesh. Four hundred participants aged 55 years and above were randomly selected, attended a health assessment session and completed a multi-indicator survey questionnaire. We developed a 30-indicator Frailty Index (FI30) to assess the participant's health status and categorized: good health (no-frailty/Fit); slightly poor health (mild frailty); poor health (moderate frailty); and very poor health (severe frailty). Pearson chi-square test and binary logistic regression analysis were conducted.

RESULTS

The participants' mean age was 63.6 years, and 61.6% of them were assessed in poor to very poor health (moderate frailty/36.3% - severe frailty/25.3%). The eldest, female and participants from lower family income were found more frailty than their counterparts. Participants aged 70 years and above were more likely (adjusted OR: 4.23, 95% CI: 2.26-7.92, p < 0.0001) to experience frailty (medical conditions) than the pre-elderly age group (55-59 years). Female participants were more vulnerable (adjusted OR = 1.487, 95% CI: 0.84-2.64, p < 0.0174) to frailty (medical conditions) than male. Also, older adults who had higher family income (Income>$473.3) found a lower risk (adjusted OR: 0.294, 95% CI: 0.11-0.76, p < 0.011) of frailty (poor health).

CONCLUSION

Our study results confirm the prevalence of frailty-related disorders in Bangladeshi older adults and highlight the importance of targeted clinical and community-led preventive care programs.

Natural regeneration potential of Madhupur National Park, Bangladesh

Natural regeneration is an essential tool to evaluate the overall health of a forest ecosystem. Natural regeneration of the tree species in Madhupur National Park showed 47 regenerating tree species among which Shorea robusta has maximum density (18,046 seedlings per ha) followed by Aporosa sp., whereas minimum density (19 seedling per ha) was recorded for Cassia nodosa, Litsea glutinosa, Grewia asiatica and Syzygium cumini, respectively. Relative density, relative frequency and relative abundance were estimated to assess the Importance Value Index (IVI) of the seedlings of different tree species. IVI of S. robusta was highest (66.25 out of 300) followed by Mallotus philippensis (27.33). G. asiatica, Derris robusta, and L. glutinosa showed the lowest IVI (0.93) among the regenerating tree species. Distribution of seedlings into different height classes showed that maximum number (31.4%) of seedlings in the height range of 50 - <100 cm. Among the recorded seedlings, Protium serratum showed maximum (11%) recruitment success. Alien invasive species, pineapple and banana based participatory agroforestry, frequent occurrence of fire, extensive collection of fuelwood and litter are the potential threats to the natural regeneration of Madhupur National Park.

Nanoassembly of gold nanoparticles: An active substrate for size-dependent surface-enhanced Raman scattering

Nanoassembly of gold nanoparticles has been achieved through a simple and facile process without using any surfactants or linkers. Atomic force microscopy confirmed assemblies of several tens of microns, whereas tiny interparticle gaps less than 5 nm was revealed by scanning electron microscopy. Such nanoassemblies with tiny interparticle gaps were found to be highly surface-enhanced Raman scattering (SERS)-active with enhancement factor in the order of 6 to 8. Contrary to usual trends in nanoparticles size dependent SERS enhancement, such 2D nanoassemblies of different sizes of nanoparticles showed relatively broadened SERS enhancement distribution. Finite difference time domain (FDTD) analysis was employed to highlight the EM-field distribution in connection to such giant SERS enhancement. In depth and hotsite-wise analysis on EM near-field distributions for monomers, dimers and septamers of 50 nm of gold nanoparticles were carried out at three specific incident polarizations (i.e. s-, 45° and p-polarizations). At s- and p-polarization the strongest hotsites were having the EM near-field distributions in the range of 124.8 and 133.3 V/m respectively with lower population of confined EM near-fields. Such correlated investigation will be indispensable to understand and interpret hierarchical and functional nanoassemblies from its unit nanoparticle blocks for the advances of technological breakthroughs.

Analgesic Effects of Pre-induction Low-dose Ketamine on Post-tonsillectomy Patients

Background: Post-operative pain management aims to decrease pain intensity with patient comfort and to improve post-operative outcome. Multimodal analgesia is currently recommended for effective post-operative pain control with lower total doses of analgesics and fewer side effects.Objective: To compare the analgesic effect of pre-induction low-dose ketamine against conventional general anaesthesia.Materials and Methods: This prospective comparative study was conducted over a period of 12 months at Combined Military Hospital, Dhaka. Two hundred and forty patients of either sex requiring tonsillectomy were divided into two groups: conventional general anaesthesia (control group) and general anaesthesia with low-dose ketamine (ketamine group). Non-invasive blood pressure, heart rate and SpO2 were recorded at regular intervals throughout the anaesthetic period. Post-operative analgesia was provided for both the groups using pethidine intramuscularly. Time to complete operation, pain intensity, time to request for first analgesia were noted and total opioid consumption and complications, if any occurred in 24 hours post-operatively, were also recorded and addressed accordingly.Results: The demographic data and mean operation time were similar in both the groups (p>0.05).Time to request for first analgesia was longer in lowdose ketamine group (mean ± SD 5.36±3.21 hours) than in control group (mean ± SD 2.49±1.53 hours) (p<0.05). Total dosage of pethidine consumption over 24 hours period was less in ketamine group with satisfactory pain relief (mean ± SD 98.73±2.60 mg) than in control group (mean ± SD 142.52±3.48 mg) (p<0.05). Post-operative complications were also less in ketamine group than control group (p<0.05).Conclusion: The result of this study suggests that pre-induction low-dose ketamine has pre-emptive analgesic effect and reduces overall post-operative opioid requirements.J Enam Med Col 2018; 8(2): 74-79

Nanowires: a new pathway to nanotechnology-based applications

The synthesis and the characterisation of silicon nanowires (SiNWs) have recently attracted great attention due to their potential applications in electronics and photonics. As yet, there are no practical uses of nanowires, except for research purposes, but certain properties and characteristics of nanowires look very promising for the future. Graphical abstractSemiconductor nanowires are attracting more and more interest for their applications in nanoscience and nanotechnology. The characteristic of the nanowires is their geometry with a diameter in the range of a few nanometers and a length far greater than their diameter. The structural defects often lead to mechanical defects. By reducing the number of defects per unit length, decreasing the lateral dimensions, crystalline nanowires are expected to be more resistant than the solid. Recently nanowires are attracting intense interest for solar energy conversion. In this review, we summarize the different methods of nanowires production and their applications. Special focus will be kept on silicon nanowires.

Investigation of Effluent Quality from an Effluent Treatment Plant of a Textile Industry, Fakir Knitwear Ltd. Narayangonj, Bangladesh

Textile industries are the major contributor to environmental pollution and health hazards by generating huge amount of effluents that contain several pollutants and coloring agents. The concentration of these pollutants can be reduced to the permissible limit with the help of an Effluent Treatment Plant (ETP). The study was conducted to observe the textile effluent management techniques of an Effluent Treatment Plant (ETP) of Fakir Knitwear Limited (FKL), Narayanganj, Bangladesh. FKL set up a biological treatment plant to treat the effluent generated by the industry. Different effluent quality parameters were investigated at different stages in ETP. The effluent of the outlet was dark colored probably because of soluble coloring materials of the effluent but it is comparatively better than that of raw wastewater. There were found higher EC values than the standards which indicated that the greater amount of salts in the water due to dumping of solid wastes and discharging of industrial effluents. The highest TDS value 2054 ppm was observed at the screening pit unit than the other parts of the ETP. The highest DO was found 4.58 ppm in clarification tank which was within the standard value of aquaculture. The study also showed that the lowest BOD (24 ppm) and COD (145 ppm) was found at the outlet which was comparatively better than others. Although the effluent from the outlet contained pollutants, these effluent quality was comparatively good than the untreated waste water discharged from the industry. After treatment, the effluent of outlet moderately ensures the standard quality for aquaculture and irrigation. The results suggested that it is obvious to run the ETP regularly to improve the quality of effluents to save our native environment from the harmful effects of wastewater.J. Environ. Sci. & Natural Resources, 8(2): 25-31 2015

Anisotropic gold nanoassembly: a study on polarization-dependent and polarization-selective surface-enhanced Raman scattering

Anisotropic nanoassembly of gold nanoparticles as SERS-active substrate self-depicting a tiny gaps at interstitials responsible for giant SERS enhancement.

Isolation and identification of diarrheagenic Escherichia coli causing colibacillosis in calf in selective areas of Bangladesh

This study was carried out to isolate, identify and characterize Escherichia coli from diarrheic calves, their prevalence and antibiotic sensitivity pattern during the period from November 2011 to December 2012. For this purpose 100 diarrheic fecal samples were collected from four different areas of Bangladesh. The samples were aseptically collected and brought to the laboratory of Medicine, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh. The organisms were identified as E. coli on the basis of cultural, morphological and biochemical characteristics. Further the isolated bacteria were confirmed by amplification of E. coli specific 16sRNA gene. The antibiotic resistant pattern of the isolates was also performed. Out of 100 samples 49 (49%) were found to be positive for E. coli. The highest prevalence was found in Shahjadpur, Sirajganj (53.33%) while lowest was in BAU, Mymensingh (40%). The antibiogram study revealed that all isolates were resistant against ampicillin, erythromycin, azithromycin and streptomycin where erythromycin was 100% resistant, whereas 100% sensitivity was found to tetracycline and gentamicin which might be the best choice of drug for the treatment of diarrheagenic E. coli causing colibacillosis in calves.DOI: http://dx.doi.org/10.3329/bjvm.v11i2.19139Bangl. J. Vet. Med. (2013).11(2): 145-149

Environmental Impact Assessment of Fish Diseases on Fish Production

The present research work was conducted from July 2008 to June 2009 to investigate intensity of infestation of parasites in freshwater fishes and the impact of fish diseases on fish production in northern region of Bangladesh. Possibility of out break of diseases due to deterioration of environmental factors of water bodies was included in this study. The diseases identified were ulcer diseases, EUS (Epizootic Ulcerative Syndrome), Ichthyophthiriasis, Trichodiniasis, Chilodoneliasis, Myxoboliasis, Dactylogyrosis, Gyrodactylosis, Argulosis, Pernicious anaemia, Red spot disease, Red Pest of freshwater eel, Mouth fungus, Branchiomysis, Abdominal dropsy and whirling disease. The infestation more occurred in young fishes than in adult fishes. The overall water qualities of water bodies fluctuated from July 2008 to June 2009. Physicochemical parameters have more or less significant combined effect on the deterioration of water quality as well as fish diseases. Gills were the most affected sites and parasites damaged gill filaments by rupturing blood capillaries, causing necrosis, coagulation and hemorrhage. The present study revealed the prevalence of different organisms in fishes, which are potential pathogen for them. Fishes were infested by parasites and other pathogens. From overall study it was observed that the parasites, bacteria and fungus were most important pathogen for outbreak of diseases. It was also observed that there was a direct relation between disease outbreak among fishes and environmental factors. Low alkalinity reduces the buffer capacity of water and badly affects the pond ecosystem, which in turn cause stress to the fish and become more susceptible to diseases. In case of low aquatic environmental temperature fish reduces metabolic activities, which in turn makes the fish more susceptible during the winter period towards parasitic infection. DOI: http://dx.doi.org/10.3329/jsf.v9i1-2.14655 J. Sci. Foundation, 9(1&2): 125-131, June-December 2011

A study of glutathione molecules adsorbed on silver surfaces under different chemical environments by surface-enhanced Raman scattering in combination with the heat-induced sensing method

In this study, surface-enhanced Raman scattering (SERS) in combination with a heat-induced sensing technique has been applied for investigating molecular orientations of glutathione molecules adsorbed on silver colloidal nanoparticles under different chemical environments, which has enabled us to further study how glutathione molecules are adsorbed on the silver surfaces. Factors that may affect the configurations of glutathione molecules adsorbed on the silver nanocolloids have been investigated. By observing the relative enhancement factors of SERS bands due to individual functional groups contributed from different terminals, the affinity between the different functional groups of glutathione and the silver surfaces under different conditions has been sorted and the orientations of glutathione molecules adsorbed on the silver surfaces have been investigated.

Development of a heat-induced surface-enhanced Raman scattering sensing method for rapid detection of glutathione in aqueous solutions

In this paper, a direct and simple detection method based on surface-enhanced Raman scattering (SERS) named "heat-induced SERS sensing method" is proposed for rapid determination of glutathione in aqueous solutions. It was found that highly enhanced SERS spectra of glutathione can be obtained if the silver colloids adsorbed with the analyte were heated up before the SERS measurement. Besides, it was revealed that silver particles with a size of approximately 60 nm are suitable for this study and that the SERS intensity is also influenced by the dropped sample volume, drying temperature, buffer concentration, and pH of the solution. It is noted that the thiol group of glutathione has a particularly strong interaction with a silver surface compared with other small biological molecules without a thiol group, validating this method to detect glutathione selectively. Under the optimal conditions, the detection of glutathione can be finished within 5 min, and the detection limit of ca. 50 nM can be reached, which is much better than the reported detection limit of glutathione (approximately 1 microM) by SERS. The enhancement factor of the proposed heat-induced SERS sensing method for the detection of glutathione is about 7.5 x 10(6). The proposed method holds a specific selectivity toward glutathione, facilitating its rapid detection in practical applications.

Characteristics of surface-enhanced Raman scattering and surface-enhanced fluorescence using a single and a double layer gold nanostructure

This paper reports the characteristics of surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) using a unique SERS-active substrate comprised of a single layer and a double layer of two-dimensional (2D) gold nanostructure. Colloidal gold nanoparticles were immobilized on a glass substrate and a multi-purpose experimental setup was adopted to obtain surface plasmon resonance (SPR), SERS and SEF on a single platform. Inhomogeneous intensity distribution was observed in correlated images of SPR and SERS. Several laser lines were used as excitation sources for further SERS measurements. Higher SERS intensities were observed with longer wavelength excitations at the same spatial position. Fluorescence measurements were carried out using 514 nm line and SEF images were obtained using the same sample. Fluorescence emissions were found to be enhanced in the presence of 2D gold nanostructure. A series of SERS spectra were recorded by conducting ensemble SERS measurements at a periodic interval of 2 microm, crossing bare substrates, the single layer and the double layer of gold nanostructure. The double layer provides higher enhancement in SERS than that of the single layer. Polarization-selective SERS measurements obtained at the single layer and double layer showed a clear difference in their dispersions. SERS intensities of the analytes adsorbed at the single layer were fitted well with cos(4)theta dependence; however, for the double layer, the relationship was quite uncertain.

Effect of zinc on growth of preterm babies

Zinc is being recognized increasingly as an important element in human growth, development and immunological function. It is probably the most intensely studied microelement in newborn nutrition. Zinc deficiency is common in young infants in the developing world and is associated with reduced immunocompetence and increased rates of serious disease. Preterm neonates are especially vulnerable because of preterm delivery and low birth weight. The preterm baby has very limited stored energy and needs an adequate supply of nutrient. Preterm infant have high zinc dietary requirements as 60% fetal zinc is acquired during third trimester of pregnancy. Low concentration of zinc was found in pre-term low birth weight babies in different studies. Studies showed that before supplementation serum zinc level in preterm low birth weight babies were 62+/-12.4 microgm/dl, 65 microgm/dl, 54+/-14.4 microgm/dl and after supplementation serum zinc level were 105.8+/-16.6 microgm/dl, 86.4+/-24.7 microgm/dl respectively. At the same time mean weight & length of supplementation and without supplementation group were 6084 gm vs. 5280 gm, 2779+/-638.7 gm vs. 2474.6+/-441.8 gm and length 23.7 cm vs. 21.4 cm, 46.49+/-2.6 cm vs. 44.1+/-2.8 cm respectively. So supplementation of zinc in preterm babies causes improved growth and development. Various reports showed beneficial effect of long supplement in early growth of pre-term babies. However long term follow up studies are needed to evaluate the beneficial effect of zinc supplementation on growth of preterm babies.

Near-field Raman imaging and electromagnetic field confinement in the self-assembled monolayer array of gold nanoparticles

Spatial distribution of surface enhanced Raman activity is visualized for two-dimensional (2D) nearly close-packed and well-ordered monolayer array of gold nanoparticles by using scanning near-field optical microscope. The 2D arrays exhibit highly nonuniform enhancement in Raman scattering, i.e., the regions along the edge of the 2D array are preferentially enhanced. We demonstrate that the spatial distribution of the localized electric field is also nonuniform and agrees well with that of the Raman enhancement.

Serum zinc level in preterm low birth weight babies and its comparison between preterm AGA and preterm SGA babies

Low birth weight (LBW) is a major child health problem in Bangladesh and continuing to great threat to child health and child survival in Bangladesh. LBW is a silent emergency but crisis is real and its persistence has profound and frightening impact on neonatal mortality. This observational study was conducted in Dhaka Shishu Hospital, Dhaka, Bangladesh during July 2004 to June 2005. Serum zinc levels were estimated between two groups: group-I preterm AGA (n=50), group II preterm SGA (n=50) babies. Blood samples were collected from the study population in neonatal unit and serum zinc levels were measured by flame atomic absorption spectrophotometry in Atomic Energy Center, Dhaka, Bangladesh. Observed data were made comparison among groups by Students 't' test. It was observed serum zinc level (60.2+/-15.2) in group I and (62.1+/-12.4) in group II. Serum zinc level was in lower limit of normal range in both groups with more lower level in preterm AGA babies but their difference was not statistically significant (p>0.05). So zinc supplementation may enhance the growth of preterm LBW babies in their early months of lives.

Manifestation of arsenicosis patients and factors determining the duration of arsenic symptoms in Bangladesh

This study analyzed a total of 1482 arsenicosis patients living in 6 of 496 upzilas (sub-districts) of Bangladesh, who were identified through household screening and then confirmed by a trained medical team headed by medical officer. Melanosis was common (97%) among them but about two-thirds (68.7%) of the patients were suffering from keratosis. Average age was 36 years and average duration of arsenic symptoms was 3 (median) years. About 50% of the patients had been drinking tubewell water more than 24 years. Melanosis was significantly associated with younger patients (P=0.031), shallower tubewell (P=0.005), and complication of conjunctivitis (P<0.001). Keratosis was also significantly associated with older age (P=0.022), shallower tubewell (P<0.001), complication of conjunctivitis (P<0.001), bronchitis (P<0.001), loss of appetite (P<0.001), and wasting (P<0.001). Duration of arsenic symptoms was significantly associated with older age (P<0.001), male (P=0.002), married (P<0.001), smoking (P=0.002), longer duration of consuming tubewell water (P<0.001), complication of conjunctivitis (P=0.002), loss of appetite (P<0.001), wasting (P=0.006), and social problem faced having arsenicosis (P=0.040). Multivariate odds ratio (OR) and 95% confidence interval (CI) indicated that keratosis (OR=2.00; 95% CI: 1.56-2.56) was significantly associated with longer duration of arsenic symptoms; loss of appetite (OR=1.40; 95% CI: 1.12-1.74) was a significant complication for longer duration. Similarly smoking (OR=1.33; 95% CI: 1.06-1.68) was positively associated with longer duration of arsenic symptom. These findings will help the policy makers of Bangladesh to understand about the factors that may affect the severity condition of the patients through prolongation of arsenic symptoms.

Levels of blood and urine chemicals associated with longer duration of having arsenicosis in Bangladesh

Arsenicosis is presently one of the significant public health problems in Bangladesh. Employing household screening of over 3.6 million people living in 6 arsenic-affected Upzilas of Bangladesh, 1,503 arsenicosis patients were identified at first and then blood and urine were collected from some of them and analyzed through laboratory techniques. As the relation between blood and urine chemicals with duration of having arsenicosis (DHA) is not clear, this study presented all findings by shorter versus longer DHA. Complications namely chronic bronchitis, conjunctivitis/congestions, weakness, and wasting were common, with relatively higher rates in longer group. Logistic regression analysis adjusted for age, sex, education, smoking, duration of drinking tube-well water, and whether any arsenicosis patients were in the family-indicated higher odds ratio (OR) of longer DHA (LDHA) in 3rd tertile with respect to GOT (OR = 2.12; 95%CI: 1.09-4.13), and blood glucose (OR = 2.00; 95%CI: 1.07-3.72) than 1st tertile. The OR of LDHA was significantly lower (OR = 0.48; 95%CI: 0.25-0.93) in 3rd tertile for triglycerides compared with 1st tertile. Albumin/globulin (A/G) ratio of 2nd tertile showed significantly lower OR of LDHA (OR=0.51; 95%CI: 0.28-0.95) than 1st tertile. Further epidemiological investigations based on a large sample, through cohort or case control studies, may be useful for validating and generalizing the results in Bangladesh.

Resistance pattern of bacteria isolated from acute respiratory tract infection (ARI) cases

Out of 350 acute respiratory tract infection (ARI) patients 110 (31.4%) were positive on culture. Among then (35.5%) yielded from upper respiratory tract infection (URI) and 64.5% yielded from lower respiratory tract infection (LRI). Predominant bacterial isolates from URI were Staph aureus (12.4%) and Strepto. pyogen (9.8%) whereas predominant agent from LRI were Strepto. pneumoniae (14.7%) and Haemophilus influenzae (8.6%). Capsular typing by polymerase chain reaction (PCR) and type specific antisera revealed that 64.7% of the isolates were type-b and rest were non-b. The most frequent resistance pattern of H. influenzae was found resistant to penicillin-ampicillin (64.7%) followed by SMX-TMP (14.7%) and tetracycline (5.9%). Among penicillin-ampicillin resistant strains, 81.8% were beta lectamase positive and 18.2% were beta lectamase negative. Among beta lectamase positive strains 66.7% were capsular type-b and 33.3% were non-b, had MICS < or = 8 microgram/ml. and < or = 4 microgram/ml. respectively. 5.9% strains of Strepto. pneumoniae was found resistant to SMX-TMP, 5.9% to penicillin-ampicillin and 2.9% to cephalexin. Common resistance pattern of Staph aureus was penicillin-ampicillin (60%), SMX-TMP (37.2%) and tetracycline-erythromycine-cephalexin (11.4%). Strepto. pyogen was found resistant to tetracycline in 12.2% cases and to SMX-TMP in 8.3% cases.