As the core equipment for biosafety monitoring, the detection sensitivity of biological alarms is closely related to particle size testing technology. Accurate particle size testing methods are required for different application scenarios, such as biological warfare agent reconnaissance and environmental pollutant monitoring, to ensure accurate identification of aerosol particles. The following analysis will be conducted from three aspects: testing principles, technical selection, and operational standards.

　　1、 The core principle of particle size testing

The biological alarm collects air samples and uses particle size distribution data to determine the presence of biological threats. The particle size of particulate matter directly affects its suspension time, diffusion range, and deposition characteristics in the air. For example, particles with a diameter less than 5 μ m can penetrate deep into the lungs and become high-risk carriers of transmission. Therefore, particle size testing needs to cover a wide range from nanometer to micrometer levels to address the size differences of different biological warfare agents, such as viruses and bacterial spores.

　　2、 Comparison of mainstream testing techniques

1. Laser particle size analysis method: Based on the Mie scattering theory, the equivalent volume diameter is calculated by measuring the scattering angle and intensity of particles on the laser. This method is suitable for particles ranging from 0.1 to 3500 μ m, with fast testing speed (single measurement<1 minute) and real-time analysis of aerosol dynamic changes. For example, the BM3001 bioaerosol alarm uses this technology, combined with ultraviolet induced fluorescence (UV-LIF) method, to achieve dual detection of particle size and biological activity.

2. Dynamic Light Scattering (DLS) method: Utilizing the Brownian motion characteristics of particles, the particle size is inferred by the fluctuation frequency of scattered light intensity. This method is particularly sensitive to nanoscale particles ranging from 0.4nm to 10 μ m and is suitable for detecting virus aerosols. However, it should be noted that DLS is prone to multiple scattering interference on high concentration samples and needs to be diluted before testing.

3. Electron microscopy method: Directly observe the morphology and size of particles through scanning electron microscopy (SEM) or transmission electron microscopy (TEM). This method can provide high-resolution images (resolution<1nm), but it requires pre-treatment such as drying and coating of the sample, and the single detection time is relatively long (>30 minutes), making it suitable for laboratory level particle size verification.

　　3、 Operational standards and optimization strategies

1. Sample collection and dilution: Use a dedicated sampler to collect aerosols and avoid environmental interference. For high concentration samples, they should be diluted at a ratio of 10-100 times to prevent instrument overload.

2. Calibration and verification: Regularly use standard particles (such as PSL microspheres) for calibration to ensure that the particle size measurement error is less than 5%. Compare the test results of different methods and establish a cross validation mechanism.

3. Environmental adaptability: In high temperature, high humidity or strong electromagnetic field environments, protective measures (such as heating and dehumidification devices, electromagnetic shielding boxes) should be taken to reduce the interference of external factors on the test.

Through precise particle size testing technology, biological alarms can achieve early warning and accurate identification of biological threats, providing solid guarantees for public safety. In the future, with the integration of nanotechnology and artificial intelligence, the accuracy and efficiency of particle size testing will be further improved.