Method for improving sensitivity of LPFG in detection of salt ion concentration

The invention discloses a method for improving the sensitivity of LPFG for detecting the concentration of salt ions, which is characterized by comprising the following steps: (1) straightening and cleaning a long-period grating, soaking the long-period grating in a salt-containing poly (diallyldimethylammonium chloride) aqueous solution, standing for 1-30 minutes, washing with water, and blow-drying with nitrogen to obtain a long-period grating; the long-period grating assembled with the poly (diallyldimethylammonium chloride) film is obtained; (2) immersing the long-period grating assembled with the poly (diallyldimethylammonium chloride) film into a salt-containing sodium polystyrenesulfonate aqueous solution, standing for 1-30 minutes, washing with water, and blow-drying with nitrogen; and (3) repeating the operation steps (1) and (2) for 10-50 times to obtain the high-sensitivity long-period grating. According to the method provided by the invention, the response sensitivity of the long-period grating to