Fabrication of an integrated piezo-electric micro-nebulizer for biochemical sample analysis

Abstract

This paper proposes a new micro-nebulizer integrating piezo-electric actuator, micro-nozzle plate, and the cavity of a micro-pump to achieve a high-quality nebulizing effect. With this micro-nebulizer, the size distribution of nebulized droplet particles is finer and more uniform than that of commercial ultrasonic and pneumatic ones. Besides, the system power consumption and volume size are lower and smaller than those of the ultrasonic and pneumatic types. Its whole size is about 18 mm × 32 mm × 35 mm in volume and power consumption is about 1 Watt. The fabrication process of a micro-nozzle plate includes multi-exposure and single develop (MESD), high-hardness nickel–cobalt (Ni–Co) alloy micro-electroplating and high-speed precise microinjection molding. A mold with hardness of Vicker (Hv) 550 is obtained. With such hardness, it endures the high-speed injection molding without deformation. The dimensions of nozzle plates are 4 mm in width, 7 mm in length 8 µm in nozzle-hole diameter and 100 µm in total thickness. The lowest thickness around a nozzle hole is 40 µm. The aspect ratio is about 5. When the working frequency of a piezo-electric micro-nebulizer is set at 16 KHz, a nebulizing rate of 1.8 cc min−1 is obtained. The developed piezo-electric micro-nebulizer at 16 KHz frequency oscillation shows an excellent mass median diameter (MMD or D[4][3]) value of 6.13 µm. This micro-nebulizer is applied to nebulize a test sample of myoglobin into a micro-droplet for the analysis of fused-droplet electrospray ionization (FD-ESI) mass spectrometry. Methyl-alcohol solvents of different consistencies are used to react with myoglobin for FD-ESI mass spectrometry analysis. The result reveals that this developed micro-nebulizer shows a better result of mass spectrometry compared to the commercial ultrasonic and pneumatic ones. This micro-nebulizer is applicable to the FD-ESI mass spectrometry analysis.