Arsenal have a far greater opportunity to beat Brighton and I am sure this will be the match that will be won by Arsenal. Brighton did play well in the previous two matches and they also defeated Man United, but Arsenal's game was far different because they had a good defense. Being in second place will definitely increase the motivation of Brighton players because they will definitely try to secure at least one point.
The match will also take place at home to Arsenal so they certainly will not let Brighton take full points. I am optimistic that Arsenal will win the match, Minamal will be created two goals in the match for Arsenal's victory.
In the last two matches Arsenal have not conceded at all this proves that Arsenal's defense is better and even they look solid in all lines there are no problems at all, as you said Arsenal has a much better chance of winning and is expected to be able to maintain a clean sheet especially playing in front of their own supporters, that is clearly more advantageous for Arsenal, but Arsenal also cannot underestimate Brighton they could give a surprise at the Emirates Stadium, seeing the opponent they will face I think Arsenal will likely win by a narrow score.
I was going to say that Arsenal have not yet played against a big and strong club, but I just remembered that their last opponent was Aston Villa, which actually is also a strong team, which Arsenal still managed to beat them regardless.
For me, indeed just as you have said, Arsenal may be really interested in keeping their clean sheet going further, and because of this, they are likely to prepare really hard for their coming encounter against Brighton tomorrow, so that they won't make any silly mistakes that Brighton could utilize to score.
But to be honest with you, I am not really interested in Arsenal keeping a clean sheet for how ever long they want to, all I am really interested in seeing is that at the end of the day, they always win their match, nothing will be more pleasing to see Arsenal lift the premiere league title for this season, they've done really well in the previous two seasons, and really deserve the title this season as a reward for their labor.