Your pedestal may be dirty if previous users have not cleaned the protein/dna off properly and it has dried on the optics.Try cleaning with water and if this does not work then clean with 0,5M HCl then with water

Hello Assyfa Atha

I agree with Paul Rutland There are other reasons as well because of which you may obtain negative results.

1. First and foremost, thoroughly clean the Nanodrop pedestal between samples and before blanking using lint-free tissues, and carefully load the sample onto the pedestal, avoiding any air bubbles. Fingerprints or dust or air bubbles on the pedestal can interfere with light transmission, causing an inaccurate blank reading.

2. If the blank solution used for calibration contains contaminants that absorb light at the measurement wavelength, it can lead to negative absorbance values when compared to the sample. So, ensure correct blanking with a fresh, clean solution identical to the sample solvent.

3. If your samples are very dilute, you should consider using a more sensitive method like Qubit. Nanodrop instruments might not be accurate for concentrations below 10ng/µl.

4. The problem could also be related to the instrument malfunction such as baseline drift. Baseline shifts due to temperature or electronic noise can cause negative readings. In such a case try to recalibrate the instrument.

5. Data processing errors could also be a cause like failing to correctly subtract the baseline from the sample spectrum resulting in negative absorbance values.

You may work on the above suggestions.

Best,

if cleaning the nanodrop does not help;

- have a look on the nanodrop manual; there is a way to check if the light bulb is still OK

- load your DNA on a gel... maybe the concentration is very low

Assyfa Atha, this may be a problem with the blank control.

When measuring nucleic acid concentrations with the Nanodrop, blank selection is crucial. Using a blank with the same composition as the sample buffer and without DNA is crucial for accurate measurements. GeneAid EB may not be suitable as a blank. We recommend using pure water or verifying the absorbance characteristics of the EB before making adjustments.

Also, check that your cuvette is clean; if necessary, rinse with HCl.

Didier Poncet & Malcolm Nobre really provided the same suggestion for you.

The same opinion with Paul Rutland , maybe you can run the instrument's diagnostics to determine if the lamp is functioning properly.