Do you know if any of the companies that make conventional reusable sensors for pH and DO are offering single-use versions? I need to specify a sensor manufacturer to our bioreactor bag supplier who can work with them to get the sensor integrated into the bag before we receive it.

Not to put too fine a point on it but you are looking for the wholly grail of single-use sensing, and you just might have found it. Industry leaders Hamilton and Mettler Toledo have both addressed this need and I have seen where Broadley James is working with Pall on a solution that was in Beta testing as of this past Spring. Here are links to more information;

Hamilton Single Use

Mettler Toledo Single Use

Broadley James Single Use