Diatoms are important for several reasons: 

1. Primary Producers: Diatoms are a type of phytoplankton and play a crucial role in the aquatic food chain. Through photosynthesis, they convert sunlight into energy, producing oxygen and serving as a food source for many aquatic organisms, such as small fish and zooplankton. 
2. Carbon Sequestration: Diatoms are involved in the global carbon cycle. As they photosynthesize, they absorb carbon dioxide from the atmosphere. When they die, their silica shells often sink to the bottom of oceans and lakes, effectively trapping carbon for long periods of time, which can help mitigate climate change. 
3. Diatomaceous Earth: When diatoms die, their silica shells accumulate on the ocean floor and form deposits known as diatomaceous earth. This material is used in a variety of industries for purposes such as: 

• Filtration: Diatomaceous earth is used as a filtration agent for water, food, and beverages, as its fine particles can trap impurities. 

• Abrasives: Due to its fine, gritty texture, it is used in products like toothpaste and metal polishes. 

• Pest Control: It is used as a natural insecticide, as the sharp edges of diatom shells can damage the exoskeletons of insects. 

• Insulation: Diatomaceous earth is used as an insulating material in some products due to its porous nature. 

However, diatoms also play a crucial role in forensic investigations and the use of scanning electron microscopes such as the Semplor NANOS can help with such investigations. 

Scanning Electron Microscopy is a powerful tool in forensic investigations of diatoms, particularly when examining cases of drowning. The Semplor NANOS SEM is capable of providing highly detailed, magnified images of diatoms, which can aid forensic scientists in identifying the species of diatoms and linking them to specific water sources. This level of detail is essential in understanding the circumstances surrounding a death and can be crucial for distinguishing between drowning and other causes of death. 

Here’s how the NANOS can be used in the forensic investigation of diatoms: 

1. Detailed Visualization of Diatom Frustules:

Diatoms have distinctive, highly intricate silica-based cell walls called frustules as shown in Figure 1. These frustules can vary in shape, size, and pattern depending on the species of diatom. SEM provides high-resolution images that allow forensic scientists to analyze these structures in great detail. 

• Identification of Species: With SEM, forensic experts can identify the specific species of diatoms present in a sample, based on the unique features of their frustules. This is important because different species of diatoms are found in different types of water (e.g., freshwater vs. marine environments). This can help establish where the person was submerged before death and whether the water source matches the location of the incident. 

• Distinguishing Diatom Types: Different water sources (e.g., rivers, lakes, oceans) have different species of diatoms, so SEM can help distinguish if a body was submerged in a specific body of water, thereby providing geographic clues. 

2. Improving Sensitivity and Accuracy:

SEM is far more sensitive than traditional light microscopy, enabling forensic investigators to detect very small numbers of diatoms in tissue samples. The Semplor NANOS has a resolution of < 8nm. This means the Nanos can very easily resolve diatoms which tend to be in the micron scale size. Since diatoms can be very tiny and may be present in low concentrations, SEM allows for the detection of minute quantities of diatoms in samples, even if the water was not rich in diatoms or the drowning occurred in a low-density environment (e.g., deep ocean or polluted water). 

• Detection in Forensic Samples: SEM can be used to analyze various tissues (when properly prepared for use under vacuum) such as the lungs, stomach, or bone marrow of the deceased, where diatoms may have been inhaled or ingested during drowning. The identification of even a small number of diatoms in these tissues can confirm that the person was alive at the time of immersion and inhaled water, thus supporting a drowning diagnosis. 

3. Diatom Identification in Complex Samples:

In a forensic setting, samples are often complex and may contain contaminants. For example, a sample may have a mixture of diatom species, pollutants, or other materials. The Semplor Nanos SEM can help separate and identify the relevant diatoms from other particles, ensuring that forensic scientists can focus on the critical evidence. 

• Accurate Sampling: SEM allows forensic scientists to examine samples with high precision, ensuring that the diatoms identified are accurately linked to the body of water and not to other sources, such as environmental contamination. 

• Improved Recovery of Diatom Evidence: The use of SEM can improve the recovery and preservation of diatom evidence from complex forensic samples, ensuring a more reliable and accurate analysis. 

4. Quantifying Diatom Numbers:

SEM can also assist in quantifying the number of diatoms in a sample. This can help forensic investigators determine the extent of immersion and whether the individual was submerged long enough for a significant number of diatoms to enter the body, which could suggest drowning. 

5. Providing Evidence in Court:

The high-resolution images produced by SEM can be used as visual evidence in court. The ability to show jurors or investigators the exact structure of diatoms found in a victim’s lungs, stomach, or other tissues can strengthen the case, providing strong visual evidence to support claims of drowning. 

Conclusion: 

Scanning Electron Microscopy (SEM) plays a vital role in the forensic investigation of diatoms in drowning cases by providing detailed, high-resolution images that allow forensic scientists to accurately identify and analyze diatoms in samples. It enhances the accuracy and sensitivity of diatom detection, allowing investigators to link specific diatom species to a water source, confirm drowning as a cause of death, and provide valuable evidence for legal proceedings.