Abstract
Law enforcement personnel have long employed luminol to detect blood samples at crime scenes. The iron (Fe2+) found in hemoglobin in human blood reacts with the -COO group of the luminol molecule to produce chemiluminescence (CL), which enables these detections. Luminol, however, apparently costs a significant amount of money, has a short shelf life, and obliterates DNA evidence in forensic investigations. As science and technology developed, luminol’s performance was improved by enhancing it with nanoparticles, a high chemiluminescence was observed when luminol interacts with blood. Platinum (PtNPs), silver (AgNPs), and gold (AuNPs) nanoparticles have showed greater improvements in increasing performance of luminol such as longer chemiluminescence duration and more intense chemiluminescence of luminol in the detection of blood. Three alternative methods such as physical, chemical, and green synthesis methods can be used to synthesize these nanoparticles. Therefore, in the current study silver nanoparticles were prepared by utilizing a green chemistry method in which extracts from the Citrus limon peels, Aloe vera leaves, Capsicum annuum, barks from Salix alba, Crinum asiaticum Linn leaves and Crinum macowanii bulb provided the reducing and stabilizing agents. The green chemistry method involves utilizing plants, bacteria, algae, fungi, and other organisms for the preparation of nanoparticles. For the biosynthesis of AgNPs, the use of plant biomass and extracts provides several benefits, including simplicity in handling, scalability, and appropriateness for large-scale production under non-sterile circumstances. According to Khunoana et al., the nanoparticles produced using green chemistry are just as effective as those produced using chemical processes, and they produce the best results for enhancing luminol chemiluminescence. One of their limitations is that they are not environmentally friendly. Transmission electron microscopy (TEM), Spectro fluorophotometer, Fourier transform infrared (FTIR), X-ray diffraction (XRD), Zeta potential, and ultraviolet/visible spectroscopy were used to characterize the nanoparticles.
The silver nanoparticles' structural composition was revealed by XRD to be face-centered cubic crystalline (Fcc). Fluorescence spectroscopy indicated that all the Ag-nanoparticles spectra have the characteristic peaks at between 400 nm for excitation and 800 nm for emission. They excite and emit at different wavelengths, and they have similar properties, and silver nanoparticles have higher fluorescence than plant extracts. When the size distribution of the nanoparticles was studied using a Zetasizer, it was discovered that the average particle sizes of all the nanoparticles fell between 70 and 92 nm. Study of the surface charge afforded zeta potential of -20, -29.7, -18.7, -19.5, -22.2, - 34.9 mV for Aloe vera leaves, Capsicum
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annuum, Crinum macowanii bulb plant, Citrus limon, Crinum asiaticum Linn leaves and barks from Salix alba respectively, at 100% intensity and pH 7.2. The prepared silver nanoparticles (AgNPs) showed UV-Vis absorption peak for surface plasmon resonance at 400-450 nm, whereas the plant crude extracts did not reveal any absorption band This proved that the synthesis of silver nanoparticles was successful. Plant extracts and silver nanoparticles both contain functional groups that were validated by FTIR; more peaks were seen in the fingerprint region with silver nanoparticles.
The prepared silver nanoparticles (1 ml) were added to 4 ml of luminol to enhance its performance, and chemiluminescence signals were viewed under dark conditions and fluorescence under 254 nm and 365 nm UV wavelengths. The same samples were viewed under complete darkness together with alternative materials (plant extracts) to luminol and luminol alone, they were used to detect commercial hemoglobin using surfaces that are common at crime scenes such as cotton pads, tile surfaces, wooden planks, dirty cloths, and furnished woods. Based on longer lasting chemiluminescence signals, the results showed that silver nanoparticles best increased the luminol signal. The plant extracts were examined for blood detection as well, and results indicated they are also promising materials for blood detection at crime scenes. Lemon extract was found to be more effective, showing higher fluorescence than luminol under UV light however more research is needed on lemon extract to isolate its chemiluminescent compounds and further modification to be able to detect blood in the dark conditions. The samples that are mostly mistaken for blood at crime scenes, such as tomato sauce, beetroot, and Congo red dye because they are similar to blood with colour were also analysed under the same condition with hemoglobin, and they produced results that are more similar to hemoglobin results.