I realise that you intend to generate noises and add them to the acquired tunnel current.
To generate noise, you can use “ColoredNoise” function from DSP System Toolbox.
To generate pink noise, you can use the following code.
pinkNoiseGenerator = dsp.ColoredNoise('Color', 'pink', 'SamplesPerFrame', length(z));
pinkNoise = pinkNoiseGenerator();
And to generate white noise you can use the “randn” function like so.
whiteNoise = noiseAmplitude * randn(size(z));
Additionally, "ColoredNoise" function can be used generate white noise as well by changing the ‘Color’ parameter to ‘white’.
To add these noises to acquired tunnel current `z` value. You can use simple array addition.
z_with_white_noise = z + whiteNoise;
z_with_pink_noise = z + pinkNoise’;
NOTE: since “z” is a row vector and the noise, we generated from “ColoredNoise” function is a column vector, we would require transposing the noise vector.
You can refer to the documentation, as shared by @prabhat kumar sharma for more information on the function. 
