فصلنامه لیزر در پزشکی
سال بیستم شماره 1 (پیاپی 87، بهار 1402)

In recent years, some non-invasive methods have been developed to assess the state of health and disease of the skin and tissues. The evaluation of patients by the doctor in terms of skin complications and recovery after laser treatment is done visually and based on experience. Therefore, it is suggested to use quantitative and instrumental methods along with the visual evaluation dependent on the doctor. This research is designed with the aim of providing an optical system based on spectroscopy and the use of mobile phones to investigate the distinction between healthy and unhealthy tissue in order to monitor and investigate the process of skin disease.

Methods & Materials: 

Diffuse reflection spectrometry and spectrum-based imaging methods have been used in this research. Analysis of spectroscopic data from a skin lesion of blood vessels as a study, a spectroscopic imaging method is presented.

spectral data of the skin were analyzed and the difference between the absorption peak of the lesion with healthy skin and the skin with lesion was determined. In the following, using this distinction, the imaging system was proposed based on the results obtained from spectroscopy. This imaging system is a primary optical arrangement to obtain an image without mirror reflection and also to remove environmental factors such as ambient light. In fact, by choosing the index wavelength and lighting the lesion, it is possible to show a better distinction between that lesion and the surrounding healthy area. Also, in this system, a mobile camera is used as a detector.

After recording the image of the lesion and the healthy skin around it simultaneously in one image, image processing and quantification can be used to detect and check tissue changes.

Photodynamic Therapy (PDT) is a treatment method based on the interaction between photosensitizers, light, and oxygen. First, a light source that is right for this method activates a photosensitizer substance that is taken up by cancer cells. This makes reactive oxygen species, which kill and stop cancer cells from spreading. Reactive oxygen species include singlet oxygen (O-2) and hydroxyl radicals (OH-), produced naturally in biological processes. These species are used as one of the therapeutic methods in cancer treatment because they can destroy cancer cells so that they can react with biological components such as lipids, proteins, and nucleic acids to damage them and accelerate cancer treatment. They are used due to their unique features, such as their large surface-to-volume ratio, light activation property, transportability in biological systems, and the ability to accumulate in the target areas of the disease. Nanoparticles in photodynamic therapy have been investigated to treat many diseases, including cancer, infections, and vascular diseases.

Methods & Materials:

 In this study, Strontium titanate nanoparticles were manufactured by solvothermal method, and for the first time the ability of nanoparticles to produce Reactive Oxygen Species including hydroxyl radical and singlet oxygen by stimulating them with UVA was investigated.

Due to their special properties, srTiO3 nanoparticles can selectively accumulate in cancer cells and generate ROS with balanced light irradiation. These ROS can damage cancer cells and eventually lead to death. The absorption spectrum of the reagent solutions showed that strontium titanate nanoparticles could make hydroxyl radicals and singlet oxygen. The ability of strontium titanate nanoparticles to produce reactive oxygen species was confirmed, and nanoparticles can be used as photosensitizers in the photodynamic therapy method for cancer treatment

Today, common protocols in cancer treatments, such as surgery, chemotherapy and radiotherapy, are hardly satisfactory due to their specific drawbacks such as surgical wound, chemotherapy drug resistance, and some chronic symptoms of radiation therapy, etc. In the meantime, photodynamic therapy has received much attention as a new method for cancer treatment with fewer side effects.

Methods & Materials:

 In this research, copper sulfide nanoparticles were made using an easy and low-cost method and its ability to detect singlet oxygen in different environments (water-ethanol ratio) was investigated.

In order to investigate the structural and optical properties of copper sulfide nanoparticles, X-ray diffraction analysis, transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectrum were analyzed. 808 nm laser (power 1 watt) was used as the radiation source. All analyzes confirmed the formation of mentioned nanoparticles and the size of copper sulfide nanoparticles was Environ 10 nm.

Experimental studies show that copper sulfide nanoparticles have an excellent photodynamic effect under 808 nm laser radiation, which can effectively produce singlet oxygen to destroy cancer cells. Therefore, copper sulfide nanoparticles can be used as a biocompatible and robust photosensitive material for efficient photodynamic therapy. Investigations show that increasing the ratio of water to ethanol decreases the accuracy of the anthracene probe in detecting singlet oxygen in the photodynamic therapy phenomenon. Therefore, ethanol solvent was selected as the best solvent for singlet oxygen production. In addition, the reproducibility and stability of the results were investigated in the ethanol medium, and the obtained results confirm the reproducibility of singlet oxygen production using copper sulfide nanoparticles.

The rapid development of infrared photonics has increased the demand for the design of high-performance optical photodetectors operating in the IR region. Photodetectors based on colloidal quantum dots, due to their extraordinary properties, such as affordable production costs, the ability to be fabricated on flexible layers, and the size-dependent band gap, have attracted wide attention in applications such as non-invasive medical diagnosis and healthcare. In this photodetector, photocurrent is a crucial factor in the medical and bio applications of photodetectors because they directly impact the device's sensitivity and performance.

Method & Materials: 

 In the study, the photocurrent is theoretically optimized and engineered by varying different design parameters such as film doping density and CQD diameter at different temperatures. To calculate the photodetector's performance parameters, one first needs to numerically solve both the Schrödinger and Poisson equations self-consistently by using the finite difference method to obtain the electron concentrations of each level, and the potential profile of a HgSe-HgTe CQDs structure and then photocurrent is calculated for the device.

The results show that with increasing the film doping density of HgSe CQDs, the photocurrent initially increases due to more available carriers for photoexcitation, but as the film doping density gets higher, after reaching a peak point, the increase in carrier concentration leads to enhanced recombination, which causes a decrease in the net photocurrent. On the other hand, increasing the film doping density of HgTe CQDs can lead to a decrease in the photocurrent density. The interplay between quantum confinement, carrier escape, and tunneling effects with increasing HgSe CQDs diameter causes the initial increase and after reaching a peak point, a subsequent decrease in the photocurrent of the photodetector. Also, with increasing the HgTe CQDs diameter, the photocurrent density of the photodetector decreases.

In general, optimizing and increasing photocurrent in medical and biological applications of infrared photodetectors improves the performance, accuracy, and efficiency of the devices, and by engineering the structure of infrared photodetectors based on colloidal quantum dots, the photocurrent of these devices can be optimized.

Piezophototronic is an emerging field that has attracted the attention of many researchers in recent years. This phenomenon is based on the simultaneous effect of light radiation and mechanical stress on the electrical transport of semiconductors. In this work, the piezo phototronic phenomenon in biological DNA chains is studied. By simultaneously investigating these two external stimuli, the best conditions for flowing electric current through DNA sequences can be obtained and used to design optical and piezoelectric (piezo phototronic) detectors.

Method & Materials: 

In this work, we study the electrical current through different DNA sequences by simultaneously investigating the effect of mechanical stress and light radiation. We use the Hamiltonian model of Peyrard, Bishop and Dauxois (PBD) modified by the effects of electric field of light radiation by laser and mechanical stress caused by an external force. Then, by obtaining the evolution equations of the system and calculating the electric current through the sequence, we study the electrical transport of the system.

The results show that pseudo-ohmic regions are observed in the current-voltage characteristic diagram through the voltage variation, which can be used for designing a trivial electrical device. Then, with increasing voltage, the slope of the current-voltage characteristic diagram changes to negative. In other words, we observe negative differential resistance (NDR) phenomenon in some parameter values. The NDR region can be used for designing controllable switches. Again, with increasing voltage, we observe that such regions repeat periodically. The highest current flows through the CG-20 bp sequence at room temperature (300K) and with increasing temperature, the current through the sequence decreases.

Mechanical stress and light radiation can be influential factors on the electrical transport of a biological system based on DNA. It can be said that by adjusting the intensity and frequency of the applied force and light radiation, the current through the system can be controlled, which is useful in designing piezo phototronic devices. Piezo phototronic devices are one of the main components of detectors and biosensors that can play a significant role in diagnosing diseases and their causes.

In recent decades, the prevalence of human diseases has increased continuously, this has led researchers to design biosensors with new technologies. Research shows that combining two-dimensional (2D) nanomaterials with noble metals significantly develops sensors' performance parameters such as sensitivity, figure of merit, and detection accuracy. 2D nanomaterials such as graphene, black phosphorus (BP), MXenes, and transition metal dichalcogenides (TMDCs), significantly improve performance parameters and protect metal layers against oxidation. Prism-based surface plasmon resonance (SPR) sensors have significant advantages over other optical sensors, including remarkable sensitivity, high accuracy and response speed, label-free detection, high resistance to environmental temperature changes, and the possibility of detecting molecules biological with low concentration and volume. In this review paper, the history and current status of plasmonic biosensors based on the Kretschmann configuration are investigated, focusing on 2D materials, and their potential applications in various fields, especially medicine, are evaluated. Moreover, the phenomenon of surface plasmon resonance and plasmons stimulation methods for sensing and biosensing purposes has been introduced. New numerical and analytical approaches for modeling plasmonic biosensors and determining their performance parameters have also been investigated. This review paper can be useful for the scientific community who are interested in research in the field of plasmonic biosensors.