Fig. 2
Reproducibility of Biological Physically Unclonable Function (Bio-PUF). a False color optical images and corresponding Bio-PUFs obtained by sampling an arbitrarily chosen T cell population every 5 min for a total of 24 h. At the beginning the T cells move randomly. However, over time they renounce their temporal motion and form stable colonies, which allows the Bio-PUFs to demonstrate reproducibility. b Temporal evolution of probability mass function (PMF) of inter-Hamming distance (Hinter) between the 1D keys obtained from two successive Bio-PUFs. c The mean of Hinter drops from ~30 to ~13, as the T cell population colonizes, allowing us to determine the threshold Hamming distance (~13) and the wait time (~20 h) before the T cell population can be used as reproducible Bio-PUF. d Time evolution of inter-correlation coefficients (CCinter) show gradual increase in correlation between the Bio-PUFs as the colony formation takes place. e Standard Barbara image (© 1994–2019 The MathWorks, Inc) is introduced as a challenge (C) to the Bio-PUFs. Responses are generated through logical XOR operation. f Mean Hinter between the responses remain below the predefined threshold ensuring the reproducibility aspect of the Bio-PUF. Inset shows the PMF of Hinter in post-colonization period
