2 sentences for 看不见 (kàn​bu​jiàn — invisible)

1. 这些细菌微小到肉眼看不见。

   zhè​xiē xì​jūn wēi​xiǎo dào ròu​yǎn kàn​bu​jiàn.

   These bacteria are so tiny that they are invisible to the naked eye.

   Source: Dong Chinese Dictionary

2. 空气中悬浮着许多肉眼看不见的微粒。

   kōng​qì zhōng xuán​fú zhe xǔ​duō ròu​yǎn kàn​bu​jiàn de wēi​lì.

   Many particles invisible to the naked eye are suspended in the air.

   Source: Dong Chinese Dictionary