Detection limit can be calculates using the following formula;

LOD= (k * sb)/m

Where k is chosen to be 2 or 3; k value 2 corresponds to a confident level of 92.1%.. k value 3 corresponds to a confident level of 98.3%. sb is the standard deviation of the blank. and m is the calibration sensitivity.. 

you can use this formula.. correlation coefficient is not useful here.. u just find the slope value from the linear plot versus concentration versus current plot.. Then run amperometry in the same conditions 10-15 blank experiment without analyte. and find the standard deviation for the background current.. choose 2 or 3.. in my opinion, 3 will be the right option due to the confidence interval of 98.3 %.. then u can find easily

Thankyou sir. how to determine sensitivity?

You are welcome... U can calculate the sensitivity using the current obtained for a particular concentration of the analyte. For further details, kindly refer the papar S.S. Nair et al. / Electrochimica Acta 54 (2009) 6837–6843. 

thanks sir,

M Amalraj can you please explain to me how I can calculate the SD of blanks when there is no response without analyte at all?

Shirin Vardak Run CV for about 25 times in blank solution and note the current values at the exact potential where you see response in presence of analyte. Calculate Standard deviations from those current values.