Great job! It is a lot of fun. I love the music and the "doodly" MS-paint art style. The controls are fluid and feel good, was able to make it to 18 on my best run before dying.
Hopefully constructive feedback:
It seems like I have to click repeatedly to propel the magnet forward, which tired out my clicking finger in a long run. The option to hold down the button instead would feel great IMO.
Also would like to see some indicator for where the positive particles are (either a mini-map, arrows, or maybe just particle effects that they spit out), because I found one strategy was to just go in a single direction until I see a positive, while amassing a horde of negatives behind me (which admittedly was very funny).
Not a simple idea: you could even have the negatives "suck in" particles that the positives "spit out," so by following the trajectory, you know where the positives are, even off screen. Would be helpful and a cool effect at the same time!
These are just some ideas for "polishing." Again, great job overall!