If the memory card can't be detected, it's impossible to recover the data in it. Don't know if you have tried your memory card in other devices such as digital camera or PC. Just plug your memory card in those listed devices, see if it can be detected. If yes, as to the lost photo data, I think you can rely on this picture recovery too called Wondershare Photo Recovery to recover photos lost. Or refer this article talking about 3 ways to recover deleted pictures from memory card for more info. If all in all the memory card is unable to be recognized, Your memory card may be corrupted, the only way to recover your picture data is to send it to a computer shop or for data recovery services.
First do not panic! It is possible to recover your pictures if you take care. Take the card from the phone (powered off) and if it has a "write protect" tab then lock it now. Do not try and write anything to the card or you risk causing more problems.
You can either plug in you camera to the PC as it should appear as a “Removable Drive” or put the card in a card reader attached to your PC.
Next, if you are comfortable with using a PC then you can download a photo recovery utility that will recover your photos from the following link: