Perhaps a scientist who combines machine technology with human life to achieve an immortal life? Is that haram?
The Quran in Surah Ali Imran states
كُلُّ نَفۡسٍ ذَآئِقَةُ الۡمَوۡتِؕ وَاِنَّمَا تُوَفَّوۡنَ اُجُوۡرَكُمۡ يَوۡمَ الۡقِيٰمَةِؕ فَمَنۡ زُحۡزِحَ عَنِ النَّارِ وَاُدۡخِلَ الۡجَـنَّةَ فَقَدۡ فَازَؕ وَمَا الۡحَيٰوةُ الدُّنۡيَاۤ اِلَّا مَتَاعُ الۡغُرُوۡرِ
Every soul will taste death, and you will only be given your [full] compensation on the Day of Resurrection. So he who is drawn away from the Fire and admitted to Paradise has attained [his desire]. And what is the life of this world except the enjoyment of delusion. (3:185)
If you analyze the first part of the ayah, you will realize that Allah has revealed every soul in this world will experience death. Thus immortality is something He has reserved for the Hereafter.
But whether it is a sin to pursue immortality or not depends on whether you believe or deny that ayah in the Quran.