TrueCrypt is not available for Android but there are plenty of alternatives with similar functionality. The best Android alternative is Cryptomator, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to TrueCrypt and 13 are available for Android so hopefully you can find a suitable replacement. Other interesting Android alternatives to TrueCrypt are Boxcryptor (Freemium), AES Crypt (Free, Open Source), DroidFS (Free, Open Source) and EDS (Encrypted Data Store) (Freemium, Open Source).
nCrypted Cloud is a Privacy, Security, and Collaboration solution that gives users full control over their personal and corporate Dropbox data. nCrypted Cloud adds client side encryption to your Dropbox existing data, and does not require you to migrate or move your files.