فصلنامه نانو مقیاس
سال دهم شماره 4 (پیاپی 40، زمستان 1402)

Bacterial infections and sepsis are among the most important and common causes of death worldwide. Statistics show that more than 18 million people worldwide get sepsis annually, and 28-50% of them die. Recent studies show that timely diagnosis and appropriate antibiotic prescription are among the most important initial measures for sepsis treatment; Despite the availability of antibiotic treatments for bacterial infections, the diagnosis of these infections is often misdiagnosed or delayed. Among the common methods of identifying bacterial infections are sample culturing, PCR-based, and immunological methods; But these methods require specialized equipment and are often time-consuming and expensive, and in many cases, they do not have proper accuracy. Therefore, using new diagnostic methods such as biosensors is especially important in cases of epidemics and deprived areas. This review article examines the necessity of using biosensors to detect pathogenic bacteria. The main focus of this paper is the review of biosensors for the detection of whole bacterial cells without the need for sample processing, and the recent developments in this field are discussed.

Porous, two-dimensional and monolayer carbon nitride in the form of C2N is a new material that is recently synthesized and has drawn attentions of researchers in nanoscience due to its interesting properties. In the current study, thermal properties of this material is investigated using molecular dynamics simulations. The effect of different lengths from 10 to 200 nm and over temperatures ranging from 200 to 600 K on the thermal conductivity are explored. The results show that the thermal conductivity of the structure is strongly dependent on the length and its temperature in that it increases by increasing the length and decreasing the temperature of the structure. Also, the thermal conductivity of the structure was investigated under both uniaxial and biaxial strains. It was interestingly observed that unlike similar 2D structures such as graphene, the thermal conductivity first increases up to strain values of 12% and 4%, respectively for uniaxial and biaxial strains which then falls to lower values than that of the strain-free counterpart. Further analysis showed that a decrease in the wrinkling of the structure occurs up to the above-mentioned strains resulting in smoothening of the structure and increment in the thermal conductivity as a result.

In the structure of the solar cell, thin silicon layers are located in the main bilayer in the form of a nanowire structure. These nanostructures enhance light absorption and convert it into electrical energy. The effective refractive index profile of silicon nanowires is used as an important property in solar cells, which can be significantly changed. These changes may be due to the change in the structure of the nanostructure, size, shape, as well as the change in the concentration of silicon nanowire particles, which leads to the improvement or reduction of light absorption and solar cell performance. In this research, the size, shape and concentration of silicon nanowires were synthesized and controlled at different times using gold catalyst and chemical vapor deposition and vapor-liquid-solid (VLS) techniques. The structural properties of the synthesized silicon nanowires were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optimal effective refractive index was found to be dependent on the length and density of the nanowires. The results show that the maximum efficiency and absorption of the solar cell occurs in the length of 2 mμ and the density ratio of 36% of silicon nanowires. The efficiency of the solar cell in this condition is equal to 9.6%, the filling factor is 66.4%, the short circuit current density in this sample is 28.253 mA.cm-2 and the voltage is 520 mV.

Two-dimensional nanomaterials have special capabilities in gas sensors due to features such as high surface-to-volume ratio and multiple active sites. In this research, molybdenum disulfide nanosheets, graphene oxide and their composites were prepared by liquid exfoliation, Hammers, and sonochemical methods, respectively. Physical properties of the prepared nanomaterials were evaluated using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Then the humidity sensors were prepared based on these materials on Si/SiO2 substrates and using copper electrodes. Due to the different types of carriers in graphene oxide and molybdenum disulfide (p-type and n-type, respectively), the current changes in different moisture percentages were obtained differently for these two sensors, and the behavior of the sensor based on the composite of these two materials was more similar to the behavior of graphene. The recovery time and response time of all three sensors were measured within 20 seconds. The results showed that the composite of graphene oxide and molybdenum disulfide, has a better humidity sensor behaviour rather than molybdenum disulfide nanosheets.

In this work, CdS quantum dots embedded in polyvinyl alcohol (PVA) polymer were prepared in colloidal form using the chemical bath deposition (CBD) method. Three different compounds were used in the chemical bath to prepare CdS quantum dots. In the first case, the ratio of Cd2+ ions was higher than that of S2- ions. In the second case, the ratio of Cd2+ ions was lower than that of S2- ions, and in the third case, the ratio of Cd2+ ions was equal to that of S2- ions. Optical properties including energy gap, and absorption and emission spectra were studied. According to the XRD spectrum, it can be said that the phase formed for CdS nanoparticles is a combination of hexagonal and zinc blende cubic structures. From the results of atomic force microscopy (AFM), it can be seen that CdS nanoparticles are embedded in the polymer matrix, and the sample prepared from Solution 2 has a more uniform distribution of particle size than the samples from the other two solutions. The TEM images showed that CdS particles are nearly spherical, and with increasing concentration of Cd2+ ions in the solution, the particle size increases. The energy gap of the samples was found to be in the range of 2.45 eV to 2.84 eV, which is larger than the energy gap of CdS bulk, i.e., 2.42 eV.