Proteinoids are artificial polymers that imitate certain characteristics of natural proteins, including self-organization, catalytic activity, and responsiveness to external stimuli. This paper investigates the potential of proteinoids as organic audio signal processors. We convert sounds of the English alphabet into waveforms of electrical potential, feed the waveforms into proteinoid solutions and record electrical responses of the proteinoids. We also undertake a detailed comparison of proteinoids’ electrical responses (frequencies, periods, and amplitudes) with original input signals. We found that responses of proteinoids are less regular and have lower dominant frequency, wider distribution of proteinoids and less skewed distribution of amplitudes compared with input signals. We found that letters of the English alphabet uniquely map onto a pattern of electrical activity of a proteinoid ensemble, that is the proteinoid ensembles recognise spoken letters of the English alphabet. The finding will be used in further designs of organic electronic devices, based on ensembles of proteinoids, for sound processing and speech recognition.

We used a high-resolution data logger, specifically the ADC-24 from Pico Technology in the UK, along with iridium-coated stainless steel sub-dermal needle electrodes from Spes Medica S.r.l. in Italy, to accurately measure the electrical activity of the proteinoids. In order to measure the potential difference, pairs of electrodes were arranged with a distance of approximately 10 mm between each electrode. All electrical activity was captured at a rate of one sample per second. The data logger captured multiple measurements, up to 600 per second, and saved their average for further study.

The BK 4060B function generator, referred to as the "device" in this paper, was used to generate electrical spikes. The device is a dual-channel function/arbitrary waveform generator. The device has the ability to generate a wide range of waveforms with high accuracy. These include sine, square, triangle, pulse, and arbitrary waveforms.  In real point-by-point arbitrary mode, the maximum waveform generation rate is 75 MSa/s. However, in direct digital synthesis mode, the maximum waveform generation rate increases to 300 MSa/s.

A setup was designed for an experiment to analyse how proteinoids respond to audio signals. The audio signals were captured using the microphone of the laptop and then processed using Matlab. The outcome of this processing yielded CSV files that consisted of a solitary column of potential values. The audio signals consisted of the letters A to Z of the English alphabet. The letters were pronounced by a male speaker using the vocal database available at the following URL: https://freesound.org/people/dersuperanton/sounds/434730/. The database contains recordings of individual letters being spoken in isolation as well as with different tones. We proceeded by using electrodes that were connected to a BK precision 4053 B transfer function in order to apply the CSV audio files to the proteinoids. The Picoscope 4000 series oscilloscope was used to record the response of proteinoids to audio signals. The data obtained was saved as CSV files for further analysis.

You can use the free programme Picoscope 7 to view the data. Available at https://www.picotech.com/downloads.