Mass of macroscopic object is determined by a suitable balance. However to determine mass of microscopic object through any normal balance is impossible. Measurement of mass at the microscopic scale is very vital as it serves powerful tool that can provide information about the molecular and atomic composition of an object. Micro-cantilevers (MCL) are used to fulfil this demand. The specifications of MCL to achieve femtogram sensitivity have been worked out. Expression for mass sensitiveness with respect to frequency has been calculated. Typical techniques used in fabrication of MCL with proper references have been mentioned. Methods to detect change in frequency or stress in MCL have been described. MCL to detect single virus cell at attogram level have been given. Progress in developing MCL for detecting zeptogram (10~(-21) g) is briefly given. Use of MCL in various fields like measurement of viscosity, density, temperature (10~(-5) K), power (pW), energy (fJ), humidity, surface examination, organic chemistry, biology, health care, magnetometery, data storage and terrorist threat detection have been discussed.
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