Chemical sensors using coated or doped carbon nanotube networks

A method for providing a sensor for presence of at least one of a first selected gas molecule and a second selected gas molecule, the method comprising:

• providing, in a chamber, first and second interdigitated electrodes, which are connected to at least one of (i) a voltage source having a controllable voltage difference and (ii) a controllable current source;
• providing a zeroth order electrically conducting network, numbered 0, of uncoated single wall carbon nanotubes (“SWCNTs”) forming a path P0 between the first and second electrodes;
• providing N electrically conducting networks, numbered n=1, . . . , N (N≧1) of single wall carbon nanotubes (“SWCNTs”) forming paths Pn (n=1, . . . , N) between the first and second electrodes, where at least one SWCNT in each of the networks no. n (n=1, . . . , N) is loaded with molecules of a selected chemical no. n;
• providing in the chamber a gas G that may have molecules of a gas constituent no. m present in a concentration Cm (m=1, . . . , M;
• M≧1), where at least one of the concentration values Cm is unknown, allowing at least one molecule of the gas G to become absorbed on at least one of the SWCNTs in each of the paths P0 in the zeroth order network and Pn in the network number n (n=1, . . . , N);
• providing an electrical parameter value (“response value”) V0(G;meas), associated with the path P0, of at least one of (i) electrical current, (ii) electrical conductance, (iii) voltage difference and (iv) electrical resistance associated with the path P0, when the gas G is present, and providing a corresponding response value Vn(G;meas), associated with the path Pn (n=1, . . . , N) when the gas G is present;
• adding a known concentration increment Δ1Cm0 of a gas constituent no. m0, selected from among the M constituents, to the gas G to provide an augmented gas G′, allowing at least one molecule of the gas G′ to become absorbed on at least one of the SWCNTs in each of the path P0 and Pn (n=1, . . . , N), and providing corresponding response values V0(G′;meas) and Vn(G′;meas) for the gas G′;
• comparing differences, Vn(G;meas)−V0(G;meas) and Vn(G;meas)−V0(G′;meas) (n=1, . . . , N) of the response values and estimating at least one of (i) concentration and (ii) concentration upper bound and (iii) concentration lower bound for at least one of the first gas molecule and the second gas molecule present in at least one of the gas G and the gas G′
• wherein the process of estimating at least one of (i) the concentration C and (ii) the concentration upper bound and (iii) the concentration lower bound comprises:
• providing an error function ε(C1, . . . , CM), defined by
• 2ε(C1, . . . , CM)=Σnwn·{Vn(G;meas)−V0(G;meas)−Σman,mCm}2+Σnw′n·{Vn(G′;meas)−V0(G′;meas)−an,m(Cm+ΔCm)}2,
• where an,m is a response value coefficient relating change in the response value Vn(G;meas) to change in the concentration Cm of the constituent no. m, ΔCm is a known concentration increment of the gas constituent no. m, added to the gas G to provide the gas G′, wn, and w′n are selected non-negative weight values, and at least one increment value ΔCm is positive;
• forming M partial derivatives of the error function 2ε(C1, . . . , CM) with respect to the concentrations C1, . . . , CM, to provide M non-homogeneous, linear equations relating the concentrations C1, . . . , CM;
• solving the M non-homogeneous linear equations to provide values, Cm(min) for the concentrations Cm as solutions of the equations;
• and
• associating at least one of the values Cm(min) with an estimate of the concentration of the constituent no. m in at least one of the gas G and the gas G′.