Writing medical or techno thrillers requires a great deal of background knowledge. But it has not got to be comprehensive as science is evolving constantly. As soon as a scientific discovery is published it can already be out of date.
There are advances that are fundamental science such as the now established structure of DNA which has lead to the identification of individuals (microbes, plants, animals and humans) through genetic fingerprinting. A number of crime writers get round having to deal with modern scientific forensic techniques by setting their stories in the past, usually before the 1960s when genetic analysis was not fully developed. Even today separate forensic laboratories in various countries use different methodologies and these will change over time.
Novelists and short story writers have the perfect get out if the science described in their work is incorrect or outdated in that it really is only fiction. But what they must ensure if they wish their work to satisfy the expectations of their readers is that it has to be believable.