Alternatively, the pH-sensing system can also be used to give an indication on the progress of wound healing because wounds do not heal properly when a pH above 8 is reached [31] and [32]. We have coloured cotton swabs with the indicator and inert dye to actually achieve two functions, namely (a) cleaning of the wound from its exudate and (b) simultaneous detection of pH. At pH values higher than 8 (which is a threshold, below healing still takes place and above the wound becomes chronic) [33] the swab turns red while at pH values below 7, the swab remains green (Fig. 6). Thus, the swabs can give valuable information on the healing progress and can act as an early indicator for possible pathogenic processes. Afterwards, a more accurate evaluation, including e.g. the identification and quantification of bacteria in the wound has to be performed using polymerase chain reaction (PCR) tests and classical immunochemical assays. It has to be mentioned that the swabs only function properly, when enough liquid is present in the wound to soak the swab; dry wounds will cause no colour changes. For use of pH electrodes on skin some researchers have recommended the use of physiological salt solution for humidification but that may well affect the pH in the wound [34]. The use of colour indicators within wound dressings for monitoring the progress of healing has also been proposed [35].